please help with Maths questions

[lurkingmum]

Much appreciated if anyone could help with following OCF FSMQ questions(Q 17s). My DD is stuck and very frustrated. I am useless at maths and have absolutely no idea... Thanks a lot.

[noblegiraffe]

I think there is some information missing from the question about the rectangular garden. I think you should have been told that the area of the lawn has to be 240m^2 otherwise the question doesn't make any sense.

[noblegiraffe]

Second one is fine. I've shown my working for finding A, then she just needs to differentiate, set to 0 to get X is about 14, then sub back into the formula for A to get A is about 700.

[lurkingmum]

Thanks a million, Noble .

[DadDadDad]

I agree with noble that the garden question must have omitted the information that the lawn has an area of 240 sq m. What this then tells you is that if the width of the lawn is x, the length of the lawn is 240/x. Adding on two lots of 3 to the width, and two lots of 5 to the length gives the dimensions of the whole garden, so A = (x + 6)(240/x + 10) = 240 + 1440/x + 10x + 60 = 10x + 300 + 1440/x.

Differentiating this should be fairly straightforward: dA/dx = 10 - 1440/x^2.

That will be zero at the minimum, so 10 = 1440/x2 which leads to x2 = 144, so x = 12.