Question

Bill weighs 80 kilograms and is gaining 2 kilograms each month. Phil weighs 65 kilograms and is gaining 5 kilograms each month. How many months, m, will it take for Bill to weigh the same as Phil?

Answer 1

Using the formula for the nth term of an arithmetic sequence we can write:
80 + (n - 1)2 = 65 + (n - 1)5
80 + 2n - 2 = 65 + 5n - 5
3n = 18
n = 6
The answer is 6 months.