Explanation for Question 24 From the Math (Calc) Section on the Official Sat Practice Test 6
Question 24 reads a customer's monthly water bill was 75, 74 2 due to a rate increase. Her monthly bill is now 79, 86 to 3 the nearest 10th of a percent. By what percent did they did the amount 4 of the customer's water bill increase. 5 Okay. So there is a percent increase formula, 6 and we're going to use that to solve this problem. 7 So that formula is going to be future value or excuse me, 8 final value minus initial value over final 9 times, 100%. And that will get you 10 the percent change. So in this case, 11 our final value is 79, 86. 12 That's the latter bill that she's left with and our initial value is 13 75, 74, since that's what she started out with. 14 So we can set up our problem like this, 15 and then don't forget that times 100%. 16 All right. So to start, let's do 79 point 86 minus 17 75.74 is equal to 4.12 over 18 79.86. 19 So then 4.12 divided by 79.86 is equal 20 to 0.05159 times 21 a hundred percent. So if you multiply that number by 100, 22 you get 5.159, 23 which is about equal to 5.16%. 24 Let's go back up to the answer choices and pick 5.16. 25 You can also round that to 5.2, because it's asking us to round to 26 the nearest 10th of a percent. So for that we pick answer choice C.