Two alloys contain zinc and copper in the ratio of 2 : 1 and 4 : 1.In what ratio the two alloys should be added together to get a new alloy having zinc and copper in the ratio of 3 : 1?

Zinc in first allow = 2/3 units;
Zinc in second alloy = 4/5 units.
copper in first alloy = 1/3 units;
copper in second alloy = 1/5 units.
Let the first and second alloys be mixed in the ratio 1 : y.
Then, {(2/3) + (4y/5)}/{(1/3 + (y/5)) = 3/1
⇒ 10 + 12y = 3 (5 + 3y)
⇒ 10 + 12y = 15 + 9y
⇒ 3y = 5
⇒ y = 5/3.
∴ Required ratio = 1 : 5/3
= 3:5