Mathematics help

[Barney Trubble]

I'm just doing a course and am stuck, of course, i've checked google for the answers but nothing makes the issues clear. I can work the answers out on a calculator but I need to know the formula that lies behind it.

 

So,

 

1) I need to find the volume of soil I dig out of a pond. The area is 4m x 2m and I have to dig 0.5 metres deep. Is the formula this:

 

4x2x0.5 so 4x2=8 x 0.5 which gives the volume as 4

 

 

2) How do I multiply this area of a room:

3.50m x 3.25m

 

I have the calculator answer but I keep getting a different answer using a manual calculation.

 

Thanks, it's been over 25 years since I was a learner, so bear with me if it's so obvious.

[View From The Top]

I'm just doing a course and am stuck, of course, i've checked google for the answers but nothing makes the issues clear. I can work the answers out on a calculator but I need to know the formula that lies behind it.

 

So,

 

1) I need to find the volume of soil I dig out of a pond. The area is 4m x 2m and I have to dig 0.5 metres deep. Is the formula this:

 

4x2x0.5 so 4x2=8 x 0.5 which gives the volume as 4

 

 

2) How do I multiply this area of a room:

3.50m x 3.25m

 

I have the calculator answer but I keep getting a different answer using a manual calculation.

 

Thanks, it's been over 25 years since I was a learner, so bear with me if it's so obvious.

 

Should have signed you up for one of my L2 courses :-)

 

If you still have my email address drop me a line and I'll help you out.

 

Volume is 4m³

 

 

Area is 11.375m²

Edited 15 May, 2012 by View From The Top

[Barney Trubble]

Thanks, I might just do that as this is a L2 course.

 

So, what path did you use to get 11.375?

 

I am using this way, I seem to remember I used at school but I can't get the answer you gave me with this method.

 

3.50

3.25 x

[View From The Top]

Thanks, I might just do that as this is a L2 course.

 

So, what path did you use to get 11.375?

 

I am using this way, I seem to remember I used at school but I can't get the answer you gave me with this method.

 

3.50

3.25 x

 

Easiest way is to just do 35 x 325 (noting that there should be 3 numbers to the right of the decimal point) which gives 11375.

 

Count in 3 places from the right, put the decimal point back and you have 11.375

 

Simple.

 

Personally I think this is the best way of doing multiplication. http://www.basic-mathematics.com/lattice-method-for-multiplication.html

[ooh it's a corner]

Volume of a regular shaped object = length x width x depth

 

(sometimes it can be easier to think in terms of a slab of concrete rather than a hole, but the methodology is the same).

 

In terms of multiplication with decimal places I always find it easier to break out the decimals so

 

3.5 x 3.25 becomes

 

(3 x 3) and (.5 x 3.0) and (3.0 x .25) and (.5 x .25)

(so whole number from left side x whole number from right side

decimal place number from left side x whole number from right side

whole number from left side x decimal place number from right side

decimal place number from left side x decimal place number from right side)

all numbers have multiplied all other numbers

 

which will give you (for reference 0.5 = a half, 0.25 = a quarter)

 

(9) and (half of 3.0 = 1.5) and (a quarter of 3.0 = .75) and (half of .25 = .125)

9 + 1.5 + .75 + .125 = 11.375

 

hope that helps but shout if not

[bridge too far]

Although I didn't have a problem with your sums, I would have found VFTT's method easier TBH

[Minsk]

Easiest way is to just do 35 x 325 (noting that there should be 3 numbers to the right of the decimal point) which gives 11375.

 

Count in 3 places from the right, put the decimal point back and you have 11.375

 

Simple.

 

Personally I think this is the best way of doing multiplication. http://www.basic-mathematics.com/lattice-method-for-multiplication.html

 

I have always found this to be the easiest way - just move the decimal points out and put them back again at the end.

[Bearsy]

It is easy you is imagining you is having sex with 3 girls and one dwarf and that is your 3.5 then you is imagining you is doing them each 3 times and 1 blow job in a night and that is ur 3.25 and then you is just calculating how many sex acts you have done (you is using a calculator for this bit) and then you is finding your answers. This is how i done all my maths at school, sometimes in exams i would draw pictures and quite often get High Marks!

[Jillyanne]

Is this not cheating???

[Ken Tone]

Is this not cheating???

 

Not unless you are married. ( or didn't you mean Bearsy?)

[Ken Tone]

Volume of a regular shaped object = length x width x depth

 

(sometimes it can be easier to think in terms of a slab of concrete rather than a hole, but the methodology is the same).

 

In terms of multiplication with decimal places I always find it easier to break out the decimals so

 

3.5 x 3.25 becomes

 

(3 x 3) and (.5 x 3.0) and (3.0 x .25) and (.5 x .25)

(so whole number from left side x whole number from right side

decimal place number from left side x whole number from right side

whole number from left side x decimal place number from right side

decimal place number from left side x decimal place number from right side)

all numbers have multiplied all other numbers

 

which will give you (for reference 0.5 = a half, 0.25 = a quarter)

 

(9) and (half of 3.0 = 1.5) and (a quarter of 3.0 = .75) and (half of .25 = .125)

9 + 1.5 + .75 + .125 = 11.375

 

hope that helps but shout if not

 

That has to be the most cumbersome calculation method I have seen for years! How on earth is that easier than 35 x 325 then put decimal point 3 places in from the right?

[ooh it's a corner]

That has to be the most cumbersome calculation method I have seen for years! How on earth is that easier than 35 x 325 then put decimal point 3 places in from the right?

 

I didnt say it was easier, just that I found it easier.

 

The problem I have always had with ignoring the decimal point and then putting it back is making sure you put it back in the right place. So, is 3.50 x 3.25 three or four decimals places.

 

Obviously it is three, before anyone shouts, but for some people they will always think it's four.

 

I was taught units, tens, hundreds and thousands in school, but today they teach little people in little jumps and bigs jumps (as they get used to units and tens).

 

it's a strange science learning things, particularly as an adult, as you will no longer have the luxury of time and repetition....

[View From The Top]

I didnt say it was easier, just that I found it easier.

 

The problem I have always had with ignoring the decimal point and then putting it back is making sure you put it back in the right place. So, is 3.50 x 3.25 three or four decimals places.

 

Obviously it is three, before anyone shouts, but for some people they will always think it's four.

 

I was taught units, tens, hundreds and thousands in school, but today they teach little people in little jumps and bigs jumps (as they get used to units and tens).

 

it's a strange science learning things, particularly as an adult, as you will no longer have the luxury of time and repetition....

 

Women will usually do it to four points as a rule as they like the symmetry such as 3.35 x 3.50

 

Men will drop the 0, as a rule, and just use 3 as if the previous examples.

 

Either way, adults find this much easier to do than other methods. They also find the lattice method of multiplication much easier than traditional, which they often have never been able to do.

 

This, of course refers to adult learners returning to education.

[bridge too far]

I didnt say it was easier, just that I found it easier.

 

The problem I have always had with ignoring the decimal point and then putting it back is making sure you put it back in the right place. So, is 3.50 x 3.25 three or four decimals places.

 

Obviously it is three, before anyone shouts, but for some people they will always think it's four.

 

I was taught units, tens, hundreds and thousands in school, but today they teach little people in little jumps and bigs jumps (as they get used to units and tens).

 

it's a strange science learning things, particularly as an adult, as you will no longer have the luxury of time and repetition....

 

I always find its helpful to do a sense check in these situations

[Ken Tone]

I didnt say it was easier, just that I found it easier.

 

The problem I have always had with ignoring the decimal point and then putting it back is making sure you put it back in the right place. So, is 3.50 x 3.25 three or four decimals places.

 

Obviously it is three, before anyone shouts, but for some people they will always think it's four.

 

I was taught units, tens, hundreds and thousands in school, but today they teach little people in little jumps and bigs jumps (as they get used to units and tens).

 

it's a strange science learning things, particularly as an adult, as you will no longer have the luxury of time and repetition....

 

It's quite simple.. If you use 3.50x3.25 then multiply 350x 325 and make sure there are 4 numbers after the point. If you use 3.5 x3.25 multiply 35 x 325 , then make sure there are 3 numbers after the point.

[Ken Tone]

I always find its helpful to do a sense check in these situations

 

Quite. Since it is a number between 3 and 4 times another number between 3 and 4, you should get an answer bigger than 9 but not as big as 16 ( 4x4) . If you get the point in the wrong place and get an answer of 1100 odd ,you know you've cocked it up.

[Barney Trubble]

Thanks to all, you've all been a great help.

 

I am getting my head around complex multiplication but it's hard work when it comes to areas, especially when the course deliberately use different measurements, so they mix in MMs, CMs and feet and then ask you to find the area of a shape that is so irregular

 

I am now moving onto some challenging stuff, such as measuring cylinders, cuboids, volumes and using PI and other strange symbols!!! 3.141 is bouncing around my head big time

 

Still, a lot of us are going to need to rearm and re-skill over the next few years, to make ourselves more employable, so it's hard work after a ten hour day, but it's good to learn after all these years.

 

Thanks for all the tips, I will get back if I am stuck again. I'd rather master how to do something manually, rather than use a calculator, as I blame the calculator for a lot of my poor maths, as I stopped thinking for myself.

 

 

 

Crikey, I take my hat off to mathematics tutors,

[Whitey Grandad]

2) is three and a half times three and a quarter, so:

 

three and a half is 7/2

three and a quarter is 13/4

multiply the two gives 91/8

which is 11 and three eighths

which is 11.375 (square metres)

 

It's difficult to write fractions so I have used words. You can easily do this calculation in your head.

[stev2001]

2) is three and a half times three and a quarter, so:

 

three and a half is 7/2

three and a quarter is 13/4

multiply the two gives 91/8

which is 11 and three eighths

which is 11.375 (square metres)

 

It's difficult to write fractions so I have used words. You can easily do this calculation in your head.

 

A good alternative but I think this really complicates things.

 

With the above simple calculation you can just about get away with doing it your way if your fraction to decimal knowledge is ok ( 3/8 = 0.375 ) but this method starts to get very confusing when decimal multiplication are more complex. VFTTs link looks by far the easiest method for any multiplication.

[Halo Stickman]

There are 3 kinds of people in this world: those that are good at maths and those that ain't

[stev2001]

There are 3 kinds of people in this world: those that are good at maths and those that ain't

[Whitey Grandad]

A good alternative but I think this really complicates things.

 

With the above simple calculation you can just about get away with doing it your way if your fraction to decimal knowledge is ok ( 3/8 = 0.375 ) but this method starts to get very confusing when decimal multiplication are more complex. VFTTs link looks by far the easiest method for any multiplication.

Fractions to decimals you can normally divide in your head for most cases. For more complicated long multiplications I just use the traditional method of putting the larger number over the smaller and multiplying the top by each digit from the lower row in succession. Then you add the number of decimal places in the two multiplicands and stick the decimal point in the answer that number of places from the right. It's amazing what calculations you can do in your head with a little practice but for exam purposes you usually have to show your working.

[tpbury]

In Oz, you get fined more if you are travelling over 13km/h over the speed limit (just completed the form declaring the ex was driving...). KM to miles is divide by 8 times by 5 - So, that's (13/8)*5. Which is 1 and 5/8 *5. Which is 5 and 25/8. Which is 8 and 1/8. Which is 8.125 mph over the limit, because 100 divided by 8 is 12.5 and it seems reasonable that .125 is the answer I'm looking for, but it's basically guessing - 'sense checking'. I was a real plodder at maths.

[skintsaint]

If f′(x)=−12x−9 and f(11) = 0, find f(x).

 

Im stuck on this carnt of a question at the moment.

[skintsaint]

f(x)=−6x²−9x+825

 

didnt take long

[Draino76]

Surely if its a pond you need to use a bucket to get the water out? Or are we referring to the soil underneath the pond?

[Special K]

Don't forget the bulking factor of the soil you dig out for the pond. Whilst it is 4m3 in the solid, when you have dug it out in the loose, you can bulk that up by about 1.5 times. (just to confuse things, like)