SOLUTION: It takes about 3 bundles of grass to weave a circular mat of diameter 1½m. How many bundles to the nearest bundle, does it take to weave a similar mat of diameter 2½m?

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Question 1205077: It takes about 3 bundles of grass to weave a circular mat of diameter 1½m. How many bundles to the nearest bundle, does it take to weave a similar mat of diameter 2½m?
Found 2 solutions by MathLover1, ikleyn:
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!
use proportion:
3%2F1.5=x%2F2.5....cross multiply
3%2A2.5=x%2A1.5
7.5%2F1.5=x
x=5
it takes 5 bundles of grass to weave a similar mat of diameter 2.5m

Answer by ikleyn(52847) About Me  (Show Source):
You can put this solution on YOUR website!
.
It takes about 3 bundles of grass to weave a circular mat of diameter 1½m.
How many bundles to the nearest bundle, does it take to weave a similar mat of diameter 2½m?
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        The solution in the post by MathLover1 is INCORRECT.
        I came to bring a correct solution. 


The proportion should relate the areas of the mats, OBVIOUSLY.

    3%2Fx = %28pi%2Ar%5E2%29%2F%28pi%2AR%5E2%29,

or 

    3%2Fx = %28%281.5%2F2%29%5E2%29%2F%28%282.5%2F2%29%5E2%29.


From this proportion

    x = 3%2A%282.5%5E2%2F1.5%5E2%29 = 8.333.


Round it to the closest greater integer number to have a necessary margin.


ANSWER.  9 bundles of grass is needed.

Solved.