Explanation for Question 31 From the Math (Calc) Section on the 2019 April Sat
Uh, number 31 we're told Anna was 99 centimeters tall. 2 The day she turned three and 106.5 centimeters tall. 3 The day she turned four. If Anna's height increases by the same amount each 4 year, between the ages of two and eight, how many centimeters tall will she 5 be by the day she turns seven. So since we're told that her height 6 increases by the same amount each year, 7 we can find how much it is increasing from year to year using this 8 information from the first sentence. So if she was 99 centimeters, 9 the day she turned three and 106.5 centimeters, 10 the day she turned four, the difference between them is going to tell us 11 how much her height increases per year. 12 So 106.5 minus 99. 13 That is 7.5 centimeters every year. 14 So now we know we want to find how many centimeters tall she will 15 be. This the day she turns seven. 16 And the last measurement we have is the day she turned four. 17 So if we find how much she increases in those three years and add 18 it to the amount that she was when she was four that'll tell us 19 how tall she was when she was seven. So between seven and four, 20 that is a difference of three years. 21 And we know her height increases at a rate of 7.5 centimeters 22 per year. So three times 7.5 is 23 22.5 centimeters. 24 That means between the time she is poor and seven, 25 her height is going to increase by 22.5 centimeters. 26 So if we take this measurement at four years old, 27 106.5 centimeters, 28 plus the 22.5, that she will increase between the years of four and 29 seven. That gives us 129 centimeters. 30 And that is how tall she will be when she is seven.