Average - Study Mode

[#111] Kunal bought 65 books for Rs. 1050 from one shop and 50 books for Rs. 1020 from another. What is the average price he paid per book?
Correct Answer

(A) Rs. 18

Explanation

Solution: Total money paid for 115 books = Rs. (1050 + 1020) = Rs. 2070 ∴ Average price paid per book = Rs. ($$frac{2070}{115}$$) = Rs. 18

[#112] Average age of ten persons learning yoga is 32 years. When the age of their instructor is added, the average age becomes 34 years. The age of their instructor is-
Correct Answer

(C) 54 years

Explanation

Solution: Age of the instructor = (34 × 11 - 32 × 10) years = (374 - 320) years = 54 years

[#113] There were 24 students in a class. One of them, who was 18 years old, left the class and his place was filled up by a newcomer. If the average of the class thereby, was lowered by one month, the age of the newcomer is-
Correct Answer

(C) 16 years

Explanation

Solution: Total age decreased = (24 × 1) months = 24 months = 2 years ∴ Age of the newcomer = (18 - 2) years = 16 years

[#114] If the arithmetic mean of seventy-five numbers us calculated, it is 35. If each number is increased by 5, then mean of new numbers is:
Correct Answer

(B) 40

Explanation

Solution: Arithmetic mean of 75 members = 35 Sum of 75 numbers = (75 × 35) = 2625 Total increase = (75 × 5) = 375 Increased sum = (2625 + 375) = 3000 Increased average = $$frac{3000}{75}$$ = 40

[#115] A student obtained 60, 75 and 85 marks respectively in three monthly examinations in Physics and 95 marks in the final examination. The three monthly examinations are equal weighted whereas the final examination is weighted twice as much as a monthly examination. His average marks in physics are-
Correct Answer

(C) 82

Explanation

Solution: Average marks in Physics $$eqalign{
& = frac{{60 imes 1 + 75 imes 1 + 85 imes 1 + 95 imes 2}}{{1 + 1 + 1 + 2}} cr
& = frac{{60 + 75 + 85 + 190}}{5} cr
& = frac{{410}}{5} cr
& = 82 cr} $$