How to formulate exponential growth?

Question

Here's my question:

A rumour spreads exponentially through a college. 100 people have heard it by noon, 200 by 1pm. How many people have heard it

a) by 3pm b) 12.30pm c)1.45pm

thanks in advance.

Answer 1

Hints:

(a) the number doubles every hour, i.e. multiplies by $2$

(b) the number multiplies by $\sqrt{2}$ every half-hour

(c) the number multiplies by $2^\frac14$ every quarter of an hour