A 60 L mixture has a milk-water ratio of 7:3. How much water to add to make the ratio 1:1?

Question

A 60 L mixture has a milk-water ratio of 7:3. How much water to add to make the ratio 1:1?

1. A. 18 L
2. B. 20 L
3. C. 22 L
4. D. 24 L (Correct answer)

Correct Answer

Option D — 24 L

Detailed Solution & Explanation

The correct answer is 24 L.

Key Points

• Split the 60 L in the ratio 7 : 3 (ten parts of 6 L each):
  • Milk = 7 × 6 = 42 L, Water = 3 × 6 = 18 L
• Adding water does not change the quantity of milk, which stays at 42 L.
• For a 1 : 1 ratio the water must also equal 42 L.
• Water to add = 42 − 18 = 24 L.

Additional Information

• The key insight in every "add one ingredient" mixture question is that the other ingredient is unchanged — fix that quantity first and everything else follows.
• Check the result: after adding, the mixture is 84 L with 42 L each, which is 1 : 1 ✓.
• Where the question instead removes and replaces part of the mixture, a different rule applies: after n replacements of quantity x from a total T, the original liquid remaining is T(1 − x/T)ⁿ.

प्रश्न (हिन्दी में)

60 लीटर के मिश्रण में दूध-पानी का अनुपात 7:3 है। अनुपात 1:1 करने के लिए कितना पानी मिलाना चाहिए?

1. A. 18 लीटर
2. B. 20 लीटर
3. C. 22 लीटर
4. D. 24 लीटर