# Math Help - simple area problems

1. ## simple area problems

Hi; question I have 25sqm to cover with paving slabs whicj are 400mmsquared. answer my answer is convert mm to m ie 0.4*0.4 = 0.16msquared then 25 / 0.16 = 156.25 slabs needed are far as I'm concerned this is correct? but I've just used an online calculator that tells me I need 150 slabs surely this is wrong? also I need to cover the same area with turf which is 1sqyard per roll. sqm to sqfeet divide by 0.0929 which gives 25 / 0.0929 = 269.1sqfeet. dividing by 9 because a yard is 9sqfeet gives 269.1 / 9 = 29.9 rolls I'm sure this is correct?Just need confirmation please.Thanks.

2. ## Re: simple area problems

In $1\text{m}^2$, there are $1000^2 \text{ mm}^2$.

In $400\text{mm}^2$, there is one paving slab. So:

$25\text{ m}^2\cdot \dfrac{1000^2\text{ mm}^2}{1\text{ m}^2}\cdot \dfrac{1\text{ paving slab}}{400\text{ mm}^2} = 62,500\text{ paving slabs}$

Each multiplication converts the units one step at a time. First, I convert square meters to square millimeters. Then, I convert 400 square millimeters to paving slabs.

3. ## Re: simple area problems

For the next one:

$1\text{ m}^2 = 100^2 \text{ cm}^2$

$2.54^2\text{ cm}^2 = 1\text{ in}^2$

$36^2\text{ in}^2 = 1\text{ yd}^2$

$1\text{ yd}^2 = 1\text{ roll}$

So, multiplying out:

$25\text{ m}^2 \cdot \dfrac{100^2\text{ cm}^2}{1\text{ m}^2}\cdot \dfrac{1\text{ in}^2}{2.54^2\text{ cm}^2}\cdot \dfrac{1\text{ yd}^2}{36^2\text{ in}^2}\cdot \dfrac{1\text{ roll}}{1\text{ yd}^2}\approx 29.900\text{ rolls}$

4. ## Re: simple area problems

Ok the paving slab question each slab is 400mmsquared therefore one slab is 0.4*0.4 = 0.16msquared surely
and 25msquared / 0.16msquared = 156.25 slabs yes?

5. ## Re: simple area problems

Originally Posted by anthonye
Ok the paving slab question each slab is 400mmsquared therefore one slab is 0.4*0.4 = 0.16msquared surely
and 25msquared / 0.16msquared = 156.25 slabs yes?
No, $400\text{ mm}^2 \neq (0.4)^2\text{ m}^2$. Instead, $400\text{ mm}^2 = 0.0004\text{ m}^2$, so

$\dfrac{25\text{ m}^2}{0.0004\text{ m}^2} = 62,500\text{ slabs}$

7. ## Re: simple area problems

I kind of see but 400mm = 0.4m yes?

8. ## Re: simple area problems

$400\text{ mm} = 0.4\text{ m}$

But, you don't have millimeters. You have square millimeters. You can think of it like this if it helps:

$400\text{ mm}^2 = 20^2\text{ mm}^2 = (20\text{ mm})^2 = (0.02\text{ m})^2 = 0.02^2\text{ m}^2 = 0.0004\text{ m}^2$

9. ## Re: simple area problems

Ok thnaks for your help I have to go I will look tomorrow.

10. ## Re: simple area problems

just can't see it you mean to tell me that to cover an area of 25msq ifeach slab costs £1 thats £62,500.
surely we have crossed wires here?

11. ## Re: simple area problems

Ok 1m = 1000mm and 1sqm = 1000*1000 = 1000000mmsq

so 1000000*25 = 25000000 / 160000 = 156.25?

12. ## Re: simple area problems

No. 1m = 1000mm, so 1sqm = 1,000,000 sq mm is true.

25,000,000 sq mm / 400 sq mm = 62,500 slabs

The issue is, you are thinking of a paving slab as something large. It is not. If the paving slab only has an area of 400 square millimeters, it is TINY. A single "slab" is approximately the size of your finger tip. It is smaller than one square inch.

13. ## Re: simple area problems

Oh i see, No the slab is 400mm*400mm = 160000sqmm.

14. ## Re: simple area problems

Originally Posted by anthonye
Oh i see, No the slab is 400mm*400mm = 160000sqmm.
Ok, that is different. In the original post, you said that a single slab is 400 square millimeters. If it is 400mm per side, then you were correct that a single slab is 0.16 square meters, so you need at least 156.25 slabs. If slabs cannot be cut into quarters, then you really need 157 slabs.

15. ## Re: simple area problems

Ok, ops sorry for the misunderstading.

thanks very much for your time on this post and for all the help.

Thank you.