In what ratio should pulses costing Rs. 15/kg and Rs. 20/kg be mixed to get a mixture worth Rs. 16.50/kg?

Problem restatement
Find the mixing ratio (cheaper : dearer) for a target mean price of Rs. 16.50 between Rs. 15 and Rs. 20.

Concept/Approach
Use alligation: Quantity ratio (cheaper : dearer) = (dearer − mean) : (mean − cheaper).

Step-by-step calculation
Ratio = (20 − 16.50) : (16.50 − 15) = 3.50 : 1.50 = 7 : 3

Verification/Alternative
Weighted average check with 7 kg of Rs. 15 and 3 kg of Rs. 20: mean = (7×15 + 3×20)/10 = (105 + 60)/10 = 165/10 = 16.50.

Final Answer
7 : 3