Robin mixes two liquids, one blue in colour and other red in

Robin mixes two liquids, one blue in colour and other red in colour in the ratio 3:1 and sells the mixture at the rate of $15 per litre, thereby making a 20% profit on his outlay. The blue liquid costs Robin $2 per litre lesser than the red liquid. How much does a litre of red liquid cost?


A) $14
B) $13
C) $12
D) $11
E) $10


Source: 4Gmat

Hi can someone share strategies and concepts on Ratios, Mixtures and Propotion