Math problem of the day

Question:
A driver travelled at 80 kph for 3 hours and 40 kph for 45 minutes. How many kilometers (d) did he travel, and what was his average speed (v) for the whole trip?

Answers variants: A. d=258; v=68.8   B. d=120; v=34.5   C. d=270; v=72   D. d=290; v=74   E. d=210; v=96


Correct answer: C. d=270; v=72
Tutorial:

First we determine the value of d, how many kilometres travelled. To do this, we can use the formula d = v*t, where d is distance, v is speed, and t is time. Taking into account that 45 minutes = 3/4 hour, and adding the two legs of the journey, we find, d = 80*3 + 40*3/4 = 240 + 30 = 270 km.
Next, we use another version of the formula, v = d/t. The time (t) of the whole trip was
3 + 3/4 = 12/4 + 3/4 = 15/4, and so the average speed (v) is given by
v = d/t = 270/(15/4) = 270*4/15 = 72 kph.
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Correct answer is (C) - d=270; v=72

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