- 1. What is the average of first 21 multiples of 7?

**Answer: Option 'B'**

**Required average = 7(1+2+....+21) / 21
(7/21)X ( (21x22) / 2 ) (because sum of first 21 natural numbers)
= 77**

- 2. In a class, the average age of 30 boys is 13 years and the average of 20 girls is 12 years. what is the average age of the whole class?

**Answer: Option 'D'**

**Total age of 50 students
(30X 13+20 X 12) = 630
Average = 630/50 = 12.6 Years**

- 3. The average age of a class of 32 students is 16 yrs. if the teacher's age is also included, the average increases by one year. Find the age of the teacher

**Answer: Option 'A'**

**Total age of students is 32 × 16 = 512 Years
Total age inclusive of teacher = 33 × (16+1) = 561
So, Teacher's age is 561-512 = 49 Yrs
There is a shortcut for these type of problems
Teacher's age is 16+(33 × 1) = 49 Years**

- 4. The average of seven numbers is 18. The average of first three numbers is 14 and the average of last three numbers is 19. What is the middle number?

**Answer: Option 'C'**

**The total of seven numbers = 7 × 18 = 126
The total of first 3 and last 3 numbers is = 3 × 14+3 × 19 = 99
So, the middle number is (126 - 99 ) = 27**

- 5. Average of five consecutive even numbers is 35. Find the greatest number in these five numbers?

**Answer: Option 'C'**

**39**

- 6. Average of 13 results is 65. If the average of first six results is 61 and average of last six results is 59 Then find the seventh result?

**Answer: Option 'C'**

**125**

- 7. The average weight of a class of 20 boys was calculated to be 58.4 kgs and it was later found that one weight was misread as 56 kg instead of 65 kg. What is the correct weight?

**Answer: Option 'C'**

**Actual total weight is (20 × 58.4 - 56 + 65) = 1177 Kgs
Actual average weight is 1177/20 = 58.85kgs**

- 8. The average of 10 numbers is 25. The average of first three numbers is 22 1/3 and that of next five is 15 1/5. If the eighth be less than the ninth and tenth numbers by 5 and 11 respectively, then the tenth number is:

**Answer: Option 'C'**

**41**

- 9. The average of 5 consecutive numbers is n. if the next two number are also included. The average will?

**Answer: Option 'B'**

**Increase by 1**

- 10. The average of marks of a student of 8 exams was 35. How many marks must be get in the next exam so as to increase his average of marks by 5?

**Answer: Option 'B'**

**80**

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