2
$\begingroup$

I'm currently studying for the SAT. I'm taking a practice quiz and came across this problem:

enter image description here

Now, using simple logic (and a bit of cheating by trial and error) we can easily determine the answer to be (D) 20 feet. This seems to be the only explanation I can find. See here. There has just always been a true mathematical explanation. I'm sure this one does too. My first thought is to use proportions but I can't seem to get it right.

So, I'm not asking for an answer here, I wanted to know how to properly do this.

1 Answers 1

3

The phrase "decreased 10 percent" means that the difference in the depths from 3pm to 4pm, which is 2 feet (from the two vertical intervals on the graph), is 10% or $\frac{1}{10}$ of the depth at 3pm. So, the depth at 3pm is $10\times 2=20$ feet and the depth at 4pm is 10% or 2 feet less, so 18 feet (choice C).

  • 0
    Ha! I feel incredibly dumb! Such an obvious question. My mistake, I was reading too far into the question.2012-01-27