Arun mixes coffee and chicory in the ratio 5:3. Then, he sells

Two ways.

First, Plugging In The Answers (PITA). I like trying B and D.
Let's say chicory costs $1 per unit.
B: Chicory costs $1 per unit. Coffee costs $1.50 per unit. The mixture costs (3*1)+(5*1.5) = 3+7.5 = $10.50. He sells the mixture for $1.65 per unit, and 8*1.65 = $13.20. That's a profit of $2.70, which is less than 28% of $10.50.
D: Chicory costs $1 per unit. Coffee costs $1.75 per unit. The mixture costs (3*1)+(5*1.75) = 3+8.75 = $11.75. He sells the mixture for $1.925 per unit, and 8*1.925 = $15.40. That's a profit of $3.65, which is more than 28% of $11.75.
B was less than 28% and D was more than 28%. We need something in between.
Answer choice C.

Second, Algebra.
Let's make Y = the cost per unit of chicory. Y(1+x) = Y+Yx is the cost per unit of coffee, where x is the percentage by which coffee costs more per unit than does chicory.
Total cost = \(5(Y+Yx)+3Y = 5Y+5Yx+3Y = 8Y+5Yx\)\(\)
Total revenue = \(8*1.1*(Y+Yx) = 8.8Y+8.8Yx\)
Total profit = \(8.8Y+8.8Yx-(8Y+5Yx) = 8.8Y+8.8Yx-8Y-5Yx = 0.8Y+3.8Yx\)
Profit/Cost = 0.28
\((0.8Y+3.8Yx)/(8Y+5Yx) = 0.28\)
\((0.8Y+3.8Yx) = 0.28(8Y+5Yx)\)
\(0.8Y+3.8Yx = 2.24Y+1.4Yx\)
\(2.4Yx = 1.44Y\)
x = 1.44Y/2.4Y = 144/240 = 72/120 = 36/60 = 6/10 = 60%
Answer choice C.