Explanation:

Compute cost of 1 kg of the mixture
The resultant mixture is sold at a profit of 20%. The selling price is Rs.96/kg
i.e., cost + 20% of cost = 1.2 (cost) = Rs.96
= cost of the mixture = 96/1.2 = Rs.80/kg.

Let the three variants be A, B, and C and let their cost per kg be Rs.60, Rs.75 and Rs.100 respectively.
The mean price falls between B and C.

Hence the following method should be used to find the ratio in which the 3 variants should be mixed.
Find out the ratio of QA : QC using alligation rule QA/QC

= 100−80/80−60 = 1/1 = 1 : 1
Step 3: Find out the ratio of QB : QC using alligation rule QBQC = 100−80/80−75 = 4/1 = 4 : 1
Step 4: QC, the resultant ratio of variant 'C' can be found by adding the value of QC in step 1 and step 2 = 1 + 1 = 2.
The resultant ratio QA : QB : QC :: 1 : 4 : 2.

Hence, option 3 is the correct answer.