Official Solution:A train traveling at a certain constant speed takes 30 seconds longer to travel 2 kilometers than it would take to travel 4 kilometers at 120 kilometers per hour. At what speed, in kilometers per hour, is the train traveling?
A. 24
B. 40
C. 48
D. 96
E. 120
Time to travel 4 kilometers at 120 kilometers per hour is \(\text{time}=\frac{\text{distance}}{\text{rate}}=\frac{4}{120} \text{hours} = \frac{4*3,600}{120} \text{seconds} = 120 \text{seconds}\);
Time to travel 2 kilometers at a regular speed is \(120+30 = 150 \text{seconds} = \frac{150}{3,600} = \frac{1}{24} \text{hours}\);
So, the speed of a train is \(\text{rate}=\frac{\text{distance}}{\text{time}}=\frac{2}{(1/24)}=48\) kilometers per hour.
Answer: C
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