A maths problem with a time limit

RabbitHutch

RabbitHutch

RabbitHutch

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Joined
24 Sep 2011
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Evening all, try your hand at this one. I found it in one of my sisters tests recently. The test stipulates 10 questions in 5 minutes, so you have 30 seconds average per question.

You are not permitted to use a calculator. Give the answer to 2 decimal places.



1. Find the area of the square.

SK8uI.png
 
By the way, the answer is each triangle is half an 8x8 square. Right angled triangles dontcha know. So the answer is 8x8x2, 128cm2.

/edit, by triangle, I mean quarter square.
 
I wish i was the type of person who could solve this fast in my mind,i would have been a world dictator by now:p Bit of an exageration but you get my point,if i even have one? it's hard to tell these days tbh.
 
Redman said:
By the way, the answer is each triangle is half an 8x8 square. Right angled triangles dontcha know. So the answer is 8x8x2, 128cm2.

/edit, by triangle, I mean quarter square.
Click to expand...

That's what I did, thought I was wrong.

I did it a longer way though, Instead I did ((8*8)/2)*4
 
8*8*2=128


About 3 seconds is more than enough time tbh.the trick with things like this is to spot the simplicity and have an intuition on best methods.
 
The inner square is half of the 16x16 square.

If you stop thinking of Pi as 3.14 (aka if you took a quarter of the outer square and times it by Pi you'd get the area of the circle) - instead think of the area of a circle as something like 0.8d^2 - it's much easier to get a feel for what Pi is. It's just a square times Pi = circle.

Apply the same to the inner square where the distance between opposite corners represents the height of the outer square, the gaps between the inner square and outer square are equal to the area of the inner square if you add them up. Ez pz.

And the maths... cmon you all have computers... 16 32 64 128 256... oh plz.

(16*16) / 2

who cares about triangles..
 
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