If the average weight of 10 students is 25 kg and that of other 10 students is 35 kg, then the average weight of these 20 students is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 30 kg
The combined average is the total weight divided by the total number of students.
Total weight of the first 10 students \(=10\times25=250\) kg
Total weight of the other 10 students \(=10\times35=350\) kg
Average of all 20 \(=(250+350)\div20=600\div20=30\) kg
Tip: When the two groups are of equal size, the combined average is just the average of the two averages: \((25+35)\div2=30\) kg. For groups of different sizes, the totals must be used.