Question 146885
1. Students buys mug, then drink. $2.99+$0.69=$3.68 (1 drink).
2. Students buys mug, then drink, then drink. $2.99+$0.69+$0.69=$4.37 for two drinks. $2.19 average (2 drinks).
3. Decreases, gets closer to $0.69. 
4. In other words, when does the average price go below $0.89.
Average Cost = (Cost of the mug + N*(Cost of Drink))/N
Where n is the number of drinks bought.
{{{A=(2.99+0.69n)/n}}}
{{{A=2.99/n+0.69}}}
{{{0.89=2.99/n+0.69}}}

{{{0.20=2.99/n}}}
{{{n=2.99/0.20}}}
{{{n=14.95}}}
We move up to the next highest integer, 15.
After 15 drinks, the student saves money.
5. We already did that in 4)

{{{A=2.99/n+0.69}}}