For every 5 blue beads used for making necklace, 3 yellow beads used. After making necklace 35 blue beads remain. So, the number should be multiples of 5. Since the ratio of yellow to blue beads are 1:4, the blue beads must be end with the multiples of 5 to match the making of necklace and the ratio. So, if there is 60 blue beads and 15 yellow beads, then 35 blue beads remains after making 5 necklace.