She told 2 friends, who told 2 friends, who told 2 friends....

Do you remember that old shampoo commercial where they said "You tell two friends and if they'll tell two friends ... Well, not only is it a marketing strategy but it shows the power of the doubling effect or exponential growth.
The formula for determining how many friends would know in 'n' number of days is really 2ⁿ-1.
Another way of determing the number of friends who know is to develop a table to show the growing pattern.

So, if this pattern continued day by day with 2 friends telling 2 more friends each day, how many days would pass before a million people would know? Try the worksheet and solution to find out.