2. Among four students sitting in a row, average age of last three students is 20 years and the average age of first three students is 21 years. If the age of first student is 26 years, then what is the age (in years) of the last student?
3. The mean of marks secured by 65 students in division A of class X is 54, 30 students of division B is 50 and that of 55 students of division C is 48. Find the mean of marks of the students of three divisions of Class X.
Median = mid value = average of 21st and 22nd value
Arranging data in increasing order we get
x f
4 6
5 4
6 5
7 4
8 6
9 9
10 8
So mid value i.e 21st and 22nd value = 8
5. Consider the following grouped frequency distribution: x f 0-10 8 10-20 12 20-30 10 30-40 p 40-50 9 If the mean of the above data is 25.2, then what is the value of p?
Mean = (sum of fixi/ (sum of f) = (8*5 + 12*15 + 10*25 + P*35 +9*45) / (8+12+10+P+9) = 25.2
(875 + 35P)/(39+P) = 25.2
P = 11
6. The average weight of Shubha, Govinda and Reshma is 65 kg. If the average weight of Shubha and Govinda be 63 kg and that of Govinda and Reshma be 70 kg, then the weight of Govinda is
7. The average of 100 items was found to be 30 . If at the time of calculation , two items were wrongly taken as 32 and 12 instead of 23 and 11 , then the correct average is
8. The average revenues of 11 consecutive years of a company is Rs 69 lakhs. If the average of first 6 years is Rs 64 lakhs and that of last 6 years is Rs 76 lakhs, what is the revenue for the 6th year?
9. The mean of marks secured by 30 students in division-A of class X is 67, 55 students of division-B is 63 and that of 40 students of division-C is 61. What is the mean of marks of the students of three divisions of Class X?
10. The mean of marks secured by 55 students in division A of class X is 58, 45 students of division B is 54 and that of 75 students of division C is 52. Find the mean of marks of the students of three divisions of Class X.