help with problem

[Monsterer]

I have no idea how to do this problem, is there some sort of formula needed?

A balloon has more air added to it such that its volume is increased by 28%. What was the percent decrease in the thickness of the rubber?

[calcguy]

Use scaling laws. Since the volume increased by 28%, the ratio of volumes is 1.28. So the scale factor is 1.28^(1/3) and the ratio of areas is scale factor squared, 1.28^(2/3) = 1.18. We must assume that the volume of the rubber (Area x thickness) remains constant, which is approximately true, and since the new area is multiplied by 1.18, the new thickness must be divided by 1.18 which gives 0.848 x old thickness. Percent decrease = 1 - 0.848 = 0.152 or 15.2%

[Monsterer]

thnk you very much, makes sense. I am a new coach for calculator and I would like to know where I can get resources to some of these questions? Are there any or is this forum the best resource to look and ask for help?

[AuSmith]

There's the page. And, here's a list of . My coach is the AMT service which provides calculator solution manuals:

AMT Test Writing Service - Number Sense, Mathematics, Science, Calculator Applications for invitational meets.
Tests plus solutions manual for Calculator Applications. Offers Number Sense: Elements of Number Sense by Jim Cummings. Contains preparatory material for the Number Sense Contest.
Andy Zapata, 675 Miller Road, Azle TX 76020
817-444-3655
E-mail: adzapata@juno.com

All the best,
Aaron