SAT Math Multiple Choice Practice Question 12: Answer and Explanation
12. The volume of a gas, V, in cubic centimeters (cc), is directly proportional to its temperature, T, in Kelvins (K). If a gas has a volume of 31.5 cc at 210 K, then its volume at 300 K would be
A. 121.5 cc
B. 49 cc
C. 45 cc
D. 22.05 cc
E. 0.805 cc
Correct Answer: C
C. Direct variation problems require a ratio — in this case, the ratio of volume to temperature.
Thus, you can write . Cross-multiply to get 210x = 9,450 and divide by 210 to get x = 45.