Multiple choice

Two alloys are both made up of copper and tin. The ratio of copper and tin in the first alloy is 1 : 3 and in the second alloy is 2 : 5. In what ratio should the two alloys be mixed, to obtain a new alloy in which the ratio of tin and copper be 8 : 3?

  1. 4 : 7

  2. 11 : 7

  3. 3 : 8

  4. Cannot be determined

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let Alloy 1 quantity = x, Alloy 2 quantity = y. Alloy 1 (1:3) has 1/4 copper, 3/4 tin. Alloy 2 (2:5) has 2/7 copper, 5/7 tin. New alloy needs tin:copper = 8:3. Tin equation: (3/4)x + (5/7)y = (8/11)(x+y). This gives 33x + 20y = 32x + 32y, so x = 4y/7. Ratio = 4:7.