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Math Help - simple area problems

  1. #1
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    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.
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  2. #2
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    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.
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    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}
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  4. #4
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    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?
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  5. #5
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    Re: simple area problems

    Quote Originally Posted by anthonye View Post
    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}
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  7. #7
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    Re: simple area problems

    I kind of see but 400mm = 0.4m yes?
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  8. #8
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    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
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  9. #9
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    Re: simple area problems

    Ok thnaks for your help I have to go I will look tomorrow.
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    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?
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  11. #11
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    Re: simple area problems

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

    so 1000000*25 = 25000000 / 160000 = 156.25?
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  12. #12
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    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.
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  13. #13
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    Re: simple area problems

    Oh i see, No the slab is 400mm*400mm = 160000sqmm.
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  14. #14
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    Re: simple area problems

    Quote Originally Posted by anthonye View Post
    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.
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  15. #15
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    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.
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