There are 30 students in a class. The average age of first 10 students is 12.5 years. The average age of the remaining 20 students is 13.1 years. The average age (in years) of the students of the whole class is
Options:
A . 12.7 years
B . 12.5 years
C . 12.9 years
D . 12.8 years
Answer: Option C Answer: (c)Using Rule 10, ( If the average of 'n1 ’ numbers is a1 and the average of 'n2 ’ numbers is a2 , then average of total numbers n1 and n2 is Average = ${n_1a_1 + n_2a_2}/{n_1 + n_2}$ )Average age = ${10 × 12.5 + 20 × 13.1}/{10+20}$ = ${125+262}/30$ =12.9 years
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