Average - Study Mode

[#71] The average of the reciprocals of x and y is-
Correct Answer

(B) $$frac{(x + y)}{2xy}$$

Explanation

Solution: Required average $$eqalign{
& = frac{{left( {frac{1}{x} + frac{1}{y}}
ight)}}{2} cr
& = frac{{x + y}}{{2xy}} cr} $$

[#72] The arithmetic mean of 15 numbers is 41.4. Then the sum of these numbers is-
Correct Answer

(D) 621

Explanation

Solution: Sum of numbers = (41.4 × 15) = 621

[#73] If the average of m numbers is n 2 and that of n numbers is m 2 , then the average of (m + n) numbers is-
Correct Answer

(B) mn

Explanation

Solution: Sum of m numbers = mn 2 Sum of n numbers = nm 2 ∴ Average of (m + n) numbers = $$frac{mn(m + n)}{(m + n)}$$ = mn

[#74] The average age of 9 students and their teacher is 16 years. The average age of the first four students is 19 years and that of the last five is 10 years. The teacher's age is -
Correct Answer

(B) 34 years

Explanation

Solution: According to the question, Average age of nine students and teacher = 16 years Then, the total average age of students and teacher = 16 × 10 = 160 And, average age of first 4 students = 19 × 4 = 76 Average age of last 5 students = 10 × 5 = 50 ∴ Teacher's age = 160 - 76 - 50 = 34 years

[#75] Total weekly emoluments of the workers of a factory is Rs. 1534. Average weekly emolument of a worker is Rs. 118. The number of workers in the factory is :
Correct Answer

(C) 13

Explanation

Solution: According to the question, Total weekly emoluments the workers = Rs. 1534 Number of workers = $$frac{1534}{118}$$ = 13