Algebra Practice

DrSteve
Sat, 10 Aug 2013 18:04:49 +0000

Let me start with some notes:

(1) In percent problems starting with the number 100 is often the quickest way to get the answer.
(2) Decreasing something by 10% is the same as taking 90% of that thing.
(3) Taking 90% of something is the same as multiplying by the decimal .9.

If you understand these notes, the problem takes a few seconds:

100.9.9 = 81. So the answer is 100 - 81 = 19%, choice (C).