Multiple choice

A mixture of 78 litres contains spirit and water in the ratio 7 : 6. When some quantity of water is added to this mixture this ratio becomes inverse. The quantity of water added

  1. 14 litres

  2. 12 litres

  3. 13 litres

  4. 15 litres
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Initial mixture: 78 litres with spirit:water = 7:6, so spirit = 7/13 × 78 = 42L, water = 6/13 × 78 = 36L. After adding x litres of water, ratio becomes 6:7 (inverse). So 42/(36+x) = 6/7. Cross-multiplying: 7×42 = 6(36+x), so 294 = 216 + 6x, giving 6x = 78, hence x = 13 litres.

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