Saves 100%

Moscow Puzzles, 184:

184. Can you get 100 percent savings?

One invention saves 30% on fuel; a second, 45%; and a third, 25%. If you use all three at once can you save 100%? If not, how much?

Ans.

184. No invention can save 100% on fuel, since energy cannot arise from nothing.

The correct calculation is not 30% + 45% + 25% = 100%, but
100% - (1 - 30%)(1 - 45%)(1 - 25%)
= 100% - (70% * 55% * 75%)
= 71.25%

This assumes the three inventions are independent in effect.

get 100% savings
saves 30% on fuel
a second, 45%; and
100%? If not, ...
since energy cannot arise from nothing
correct calulation
This assumes ...