How much water must be added to 100 ml of 80 per cent solution

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How much water must be added to 100 ml of 80 per cent solution of boric acid to reduce it to a 50 per cent solution ?

1. 30 ml
2. 40 ml
3. 50 ml
4. 60 ml

Correct Option: D

Let m ml of water be added.

∴	20 + m	× 100 = 50
	100 + m

⇒ 40 + 2m = 100 + m
⇒ m = 60 ml