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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.

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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.

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  • $\begingroup$ Please tell me why is my approach wrong? $\endgroup$
    – Siberan Jonah
    Commented Apr 13, 2018 at 4:16
  • $\begingroup$ 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. $\endgroup$
    – dan post
    Commented Apr 13, 2018 at 7:27

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