In what ratio must water be added to spirit to gain 25%

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In what ratio must water be added to spirit to gain 25% by selling it at cost price?

1. 1 : 4
2. 4 : 1
3. 3 : 4
4. 4 : 3

Correct Option: A

Let cost price of spirit be Re. 1 per liter.
Then SP of mixture = Re. 1 per liter
Gain = 25%
So, CP of mixture = 1 × (100 / 125) = Re. 4 / 5
We assume that CP of water is zero.
Using allegation rule on cost price,
Water should be mixed to spirit in the ratio (1 / 5) : (4 / 5) or 1 : 4