Explanation for Question 11 From the Math (Calc) Section on the Official Sat Practice Test 9
Question 11 asks us plant a is currently 20 centimeters tall 2 and plant B is currently 12 centimeters tall. 3 The ratio of the Heights of plant a to plant B is equal to 4 the ratio of the Heights of plant C to plant D if plant C 5 is 54 centimeters tall, what is the height of plant D in centimeters? 6 So this is a word problem. And the best strategy that I would recommend 7 for this one is to either draw a picture to kind of visualize what's 8 happening and or to do your best to convert these words into essentially 9 mathematical numerical equations that we can work with. 10 So let's do both let's first picture. 11 We've got plant a, and this is its height. 12 It's 20 centimeters tall plant B. 13 So this is a plant B is right here and it's shorter. 14 It's about 12 centimeters tall. 15 And it says that the ratio of the Heights of plant a to plant 16 B is equal to the ratio of the Heights of plant C to plant 17 D. So setting up a ratio, 18 we've got a over B is equal to C over D and 19 we can plug in for a and B because we have that we have 20 20 over 12 is equal to C over D. 21 Now reading the next sentence. If plants see is 54 centimeters tall, 22 what's the height of plant D. So now we have all that we need 23 to solve. The problem we have 20 over 12 is equal to C over 24 D and we can plug in 54 for C because we know that C 25 is 54 centimeters tall. Now we're solving for D and we can do this 26 easily using cross multiplication. 27 So we have 20 times D is equal to 20 D and then we 28 have 12 times 54, which is equal to 648. 29 And then to get D we'll divide both sides by 20, 30 and we'll be left with 32.4 that's 31 answer choice a.