to save fuel on the 240 km trip to the cottage, the Nakamura family reduce their usual average speed by 20 km/h. this lengthens their journey by 1 hour. what is the slower average speed?

Question

i was told this question is not complete to answer? is that true?

Answer 1

normal speed ---- x km/h
time at normal speed = 240/x hours

reduced speed --- x-20 km/h
time at reduced speed = 240/(x-20)

solve:
240/(x-20) - 240/x =1

hint: multiply each term by x(x-2)