# Average (3)

1. A car owner buys diesel at Rs.7.50, Rs. 8 and Rs. 8.50 per litre for three successive years. What approximately is the average cost per litre of diesel if he spends Rs. 4000 each year?
1. Rs. 8
2. Rs. 7.98
3. Rs. 6.2
4. Rs. 8.1

Explanation :-

Total amount spent = Rs. (3 x 4000) = Rs. 12000.
Total quantity of petrol = (4000/7.50) + (4000/8) + (4000/8.50) = 4000[(2/15) + (1/8) + (2/17)] = (76700/51)
Average cost = (12000/(76700/51) ) = (12000*51)/76700 = 7.98

2. A family consists of two grandparents, two parents and three grandchildren. The average age of the grandparents is 67 years, that of the parents is 35 years and that of the grandchildren is 6 years. The average age of the family is
1. 32 2/7 years
2. 31 5/ 7 years
3. 28 1/7 years
4. 30 5/7 years

Explanation :-

Total age of the grandparents = 67 × 2 =
Total age of the parents = 35 × 2
Total age of the grandchildren = 6 × 3
Average = [ ( 67 × 2 ) + ( 35 × 2 ) + ( 6 × 3 ) ] / 7 = 31 and  5/7

3. The average weight of 16 boys in a class is 50.25 kg and that of the remaining 8 boys is 45.15 kg. Find the average weights of all the boys in the class.
1. 48.55
2. 42.25
3. 50
4. 51.25

Explanation :-

Average = [(16*50.25) + (8* 45.15)] /(16 + 8)
Average = (804 + 361.20)/24 = 48.55

4. A library has an average of 510 visitors on Sundays and 240 on other days. What is the average number of visitors per day in a month of 30 days beginning with a Sunday?
1. 290
2. 304
3. 285
4. 270

Explanation :-

A month Starting with sunday has 5 sundays therefore other days = 30 – 5 = 25
Visitors on 5 sundays = 5 * 510
Visitors on other 25 sundays = 210 *25
[(510 × 5) + (240 × 25)] / 30 8550/30 285

5. A student’s mark was wrongly entered as 83 instead of 63. Due to that the average marks for the class got increased by 1/2. What is the number of students in the class?
1. 45
2. 40
3. 35
4. 30