In a family of 4 adults and some minors, the average consumption of rice per head per month is 8.5 kg, while the average consumption for adults is 10 kg per head and for minor it is 5.5 kg per head. The number of minors in the family is:

Let the number of minors be x.
Average food consumption for 4 adults + x minors = 8.5 kg
Then, Total food consumption for (x+4) people = 8.5(x+4) = 8.5x+34 kg
Average food consumption for 4 adults = 10 kg
Total food consumption for 4 adults = 40 kg
Average food consumption for x minors = 5.5 kg
Total food consumption for x minors = 5.5x kg
Then, 5.5x+40 = 8.5x+34
=> 3x = 6 => x = 2
Therefore, Number of minors = 2.