An alloy contains tin, copper and zinc in the ratio of 4 : 6 : 5. Find the quantity of copper to be added to 120 kg of this alloy to form a new alloy in which the ratio of the above elements in the same order is 4 ∶ 7 ∶ 5?

This question was previously asked in

DSSSB PGT Maths Female General Section - 10 July 2021 Shift 1

- 16 kg
- 20 kg
- 10 kg
- 8 kg

Option 4 : 8 kg

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**Given:**

The ratio of tin, copper and zinc in the ratio of 4:6:5 respectively.

Total quantity of Alloy = 120 kg.

**Calculation:**

Tin = (4/15) × 120 = 32 kg.

Copper = (6/15) × 120 = 48 kg.

Zinc = (5/15) × 120 = 40 kg.

If we add "x" kg of copper to the alloy then it's ratio = 4 : 7 : 5

⇒ (New quantity of copper)/(New quantity of Alloy) = 7/(4 + 7 + 5)

⇒ (48 + x)/(120 + x) = 7/16.

⇒ 16x + 768 = 7x + 840

⇒ 9x = 72

⇒ x = 8 kg

**∴ Option D is correct.**

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