Question

Destiny designs necklaces. She uses between 15 and 20 yellow and blue beads in a ratio of 4 yellow beads to 5 blue beads. I want to know how many yellow beads and blue beads are needed for this problem.

Answer 1

Well, the ratio of yellow beads to blue beads is 4:5. The best way I think is to guess and check multiplying the ratio by integers. You need between 15 and 20.
4 : 5 ( = 9 too little )
8 : 10 ( = 18 just right)
12 : 15 ( = 27 too much)
So per necklace, 8 yellow beads and 10 blue beads would be needed. 
I hope this helps :-)