# A Milk solution of 60 litres contains..

A Milk solution of 60 litres contains 80% milk. How many litres of another milk solution containing 90% milk should be added to make an 84% milk solution? [Ans: 40 lit]

I tried: $\dfrac {80}{100}\times \dfrac {M}{60}$

$\dfrac {M}{25}$

calculation of second sentence:

$\dfrac {M}{60}\times \dfrac {84}{100}$

$\dfrac {21 M}{1500}$

calculation of first part in second sentence:

$\dfrac {M}{60}\times \dfrac {90}{100}$

Final equation: $\dfrac {M}{60}\times \dfrac {90}{100} = \dfrac {M}{25} - \dfrac {21 M}{1500}$

I gone too far, is my approach right or wrong? if wrong, tell me the correct procedure.

Work with the percentages of volume. Note that "of" usually means multiplication. The initial percentage-volume plus the added percentage-volume will equal the resultant percentage-volume: $$60*\frac{80}{100}+n*\frac{90}{100}=(60+n)*\frac{84}{100}$$ You should be able to take it from there.
• To start with , it appears you were dividing the percentage by the volume, instead of multiplying. Also, you inserted the variable $M$ where no unknowns are present. My first term is for the first sentence. Commented Apr 13, 2018 at 7:27