One bus leaves a depot every 15 minutes and another every 25 minutes. If both leave together, after how many minutes will they next leave together?

Correct answer to question 119 (Arithmetic Reasoning): 75 minutes

Method

They coincide at the least common multiple of 15 and 25. The multiples of 25 are 25, 50, 75, and 75 is the first that 15 also divides. Multiplying the two intervals gives 375, a common multiple but not the least.