a) 9
b) 10
c) 11
d) 12
Sum of 10 even numbers = 10 * 11 = 110
Average = 110/10 = 11
2.The average of 11 numbers is 10.9. If the average of first six is 10.5 and that of the last six is 11.4 the sixth number is?
a) 9.5
b) 10.5
c) 11.5
d) 12.5
1 to 11 = 11 * 10.9 = 119.9
1 to 6 = 6 * 10.5 = 63
6 to 11 = 6 * 11.4 = 68.4
63 + 68.4 = 131.4 – 119.9 = 11.5
6th number = 11.5
3. The average of first ten prime numbers which are odd is?
a) 13.8
b) 14.8
c) 15.8
d) 16.8
Sum of first 10 prime no. which are odd = 158
Average = 158/10 = 15.8
4. The average of first 10 natural numbers is?
a) 3.5
b) 4.5
c) 5.5
d) 6.5
Sum of 10 natural no. = 110/2 = 55
Average = 55/10 = 5.5
5. The average of first 10 odd numbers is?a) 9
b) 10
c) 11
d) 12
6. The average of first 10 prime numbers is?
a) 9.9
b) 10.9
c) 11.9
d) 12.9
Sum of 10 prime no. = 129
Average = 129/10 = 12.9
7. The average age of three boys is 15 years and their ages are in proportion 3:5:7. What is the age in years of the youngest boy?
a) 6
b) 7
c) 8
d) 9
3x + 5x + 7x = 45
x =3
3x = 9
8. The average of 1st 3 of 4 numbers is 16 and of the last 3 are 15. If the sum of the first and the last number is 13. What is the last numbers?
a) 5
b) 6
c) 7
d) 4
A + B + C = 48
B + C + D = 45
A + D = 13
A – D = 3
A + D = 13
2D = 10
D = 5
9. The average of 9 observations was 9, that of the 1st of 5 being 10 and that of the last 5 being 8. What was the 5th observation?
a) 6
b) 7
c) 8
d) 9
1 to 9 = 9 * 9 = 81
1 to 5 = 5 * 10 = 50
5 to 9 = 5 * 8 = 40
5th = 50 + 40 = 90 – 81 = 9
10. The average of 10 numbers is calculated as 15. It is discovered later on that while calculating the average, one number namely 36 was wrongly read as 26. The correct average is?
a) 14
b) 16
c) 18
d) 20
10 * 15 + 36 – 26 = 160/10 = 16