Question 836654
You need to buy a multiple of 10 blue balls, since the total is a whole dollar amount. Every 10 balls costs $1.


Also, the cost of the red and yellow balls is a multiple of 3 dollars. Since *[tex 100 \equiv 1 \pmod 3], we need to buy either 10, 40, or 70 blue balls.


The average cost/ball is $1, so we'll probably be buying lots of blue balls. Suppose we buy 70 blue balls for $7. Then we have $93 to buy 30 balls, which occurs when we buy 29 yellow balls and 1 red ball. Therefore we buy 70 blue balls, 29 yellow balls, and one red ball.