How many mL of a stock 50% (w/v) KNO3 solution are needed to prepare 250 mL of a 20% (w/v) KNO3 solution?

100ml of a stock 50% KNO3 solutions are needed to prepare 250ml of a 20% KNO3 solution.

Explanation:

In the given question it is mentioned that

S1=50%

V2=250ml

S2 = 20%

We all know that

V1S1=V2S2

∴V1 = V2*S2:S1

∴V1 = V2S2*1/S1

∴V1 = 250*20:50

∴V1 = 100ml