Denise is selling roses. She sold 3 for $5 and 5 for $7. What will Denise charge for 12 roses if she keeps selling roses at the same rate?

$20

Explanation: First ask yourself how many groups of 5 can go into 12: 2. If Denise sells 2 groups of 5 then there will be 2 flowers left over, but Denise does not sell flowers in groups of 2. If Denise sells 1 group of 5 then there will be 7 flowers left over, which is still not divisible by three. Therefore, Denise must sell 4 groups of 3 for there to be 12 flowers. $5 x 4 = $20