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.

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**

3.

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**

4.

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**

5.

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**

6.

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**

7.

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**

8.

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**

9.

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

**Answer: Option 'C'**

**39**

10.

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

**Answer: Option 'C'**

**39**

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