Explanation for Question 18 From the Math (Calc) Section on the 2018 March Sat
Question 18 says a sample of 609th graders was selected at 2 random and asked how much time they spend on homework. 3 Each day of the ninth graders selected 220 spend, 4 less than two hours on homework each day. 5 If the conclusion was drawn that approximately 1.3, 6 5000009th graders spend less than two hours on homework each day, 7 which of the following is closest to the population in millions of ninth graders. 8 So what we need to do here is set up to ratios 220 out 9 of 600, which is the number of ninth graders in the sample 10 who said they spend less than two hours on homework each day. 11 And we're going to set that equal to 1.3, 12 5 million over X million. 13 And now all we have to do is sell for ax to find the 14 total population of ninth graders. 15 So to do that, I'm going to start by cross multiplying 600 times 1.35 16 mil is equal to 220 X, 17 and then I can divide both sides by 220. 18 If you plug this left part into your calculator, 19 you'll find that X is equal to 3.68, 20 which means that 300 or 3.6, 21 8000009th graders, 22 uh, compose the population, which is answer choice.