Maths Problem

[sophie_1003]

Couldn't find a good place to put this but I thought it sounded like maths homework so here we go- I have a balloon that has (when blown up) a circumference of 37 inches; I want to cover it with lace doilies; how much area laid out flat will the doilies need to cover in order to fully cover the balloon? TIA

[bibblebub]

435.8 square inches

[sophie_1003]

Ok; so if I lay out my doilies in a sort of square and measure two sides then times them together that will give me the area of doilies I've got (am trying to work out if I need more doilies!)

[bibblebub]

yes basically

[sophie_1003]

Ahh thank you! Am feeling mathematically challenged at the moment!

[jno]

remember that balloons aren't flat so you're going to end up with some overlapping of doilies if you want to cover it completely; which means you may need mroe doilies than you think.

[Prudie]

Having spent a while typing this out in Word I'm still going to post even though bibble's given you the answer. Good luck with it sophie. (that n is pi in Word !)

The formulae you need are surface area (SA) of a sphere and circumference(C) of a circle to find your radius which are
SA = 4πr² & C=2πr
You know 37 =2πr so radius is 37/2π, putting that in the SA formula gives you
SA= 4 x π x (37/2π²) which cancels out to give
SA = 37²/π which is roughly 436 square inches

Now it’s up to you because it depends on the size of the doileys (and also of course a balloon is not a perfect sphere)

[factor-fiction]

Bibblebub's answer is correct- assuming the balloon is a perfect sphere. If it's a sausage shape the answer will be quite a bit different

[bibblebub]

i used:

c=π d => d = c/π

surface area = π d² = π (c/π)² = c²/π

[sophie_1003]

Thanks all; it's one of the punch ball balloons so is more of a sphere than most balloons; and had thought about overlap but just wanted a rough idea of how many more doilies I'd need!