The ratio of sapphire in the bag is 2:5, and there are 25 emeralds.

Q: How many stones of which color can be added to make the ratio 1:3?

Solution:

Existing sapphire: 25×2/5= 10.

1) If the ratio of blue to green is 1:3,

There are 10×3=30 emeralds.

Need to add greenstone: 30-25=5.

2) If the ratio of green to blue is 1:3,

There are 25×3=75 sapphires.

Need to add sapphire: 75- 10=65.