Explanation for Question 30 From the Math (Calc) Section on the 2019 April Sat
And 30, we were told to Humboldt sold X cell phones in 2013 and 2 2014, that increases to one 28% greater. 3 And in 2015, that increases to 29% greater than 2014. 4 We want to know which expression represents the number of cell phones he sold 5 in 2015. So the first thing you need to know is the equation for 6 percentages, and you always take the starting value. 7 So in this case, it's an X multiplied by one plus or minus 8 the percentage as a decimal. 9 So first we can find the amount he sold in 2014. 10 So we're going to take the original value X and multiply by one. 11 We determine if it's a plus or minus based on whether we are increasing 12 or decreasing. So since it is a 128% increase 13 because of the word greater, we're going to use a plus sign there, 14 and then we need to convert the percentage to a decimal. 15 So 128% as a decimal is 1.2. 16 It, so the amount that he sold in 2014 is going to 17 be 2.28 X. 18 We aren't done yet though, because we want to find the amount he sold 19 in 2015, which is 29% greater than he sold in 20 2014. So that means our new starting value is going to be 21 2.28 X. 22 We can't just have an X there because we are starting from 2014. 23 And we found that the amount at 2014 was 2.28 X. 24 So now we multiply by one. 25 We are increasing again. So one plus, 26 and then we need to convert 29% to a decimal. 27 So that is 0.29. 28 So that means that the amount he sold in 2015 is going to be 29 equal to 2.28 X times 1.29. 30 And that is deep.