Question 7
A dog barks every $b$ minutes and a cat meows every $m$ minutes, where $b,m$ are primes satisfying $1\le b\le10$ and $10\le m\le20$. What is the greatest number of simultaneous calls in two hours? Timing clarification, as intended by the supplied solution: both start together at time $0$; count calls at $0<t\le120$, excluding the starting call.
