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Aptitude Day 161

Problems on Average:

1. The average weight of 15 boys in a class is 45.5 kgs and that of the remaining 10 boys is 50kgs. Find the average weight of all boys in the class.

Solution:
                 Average = [45.5(15)+ 50(10)] / [15+10]
                                 = [682.5 +500]/ 25
                                 = 1182.5/25
                                 = 47.3.

2. A car owner buys petrol at the cost of 6.50, 7 and 8 per litre for 3 successive years. What approximately is the average cost per litre of petrol if he spends 5000 each year?

Solution:
                 Total petrol consumed in 3 years = (5000/6.50) + (5000/7) + (5000/8)
                                                                             = 5000 [ (2/13) + (1/7) + (1/8) ]
                                                                             = 5000[307/728]
                                                                             = 191875/91 litres.

                Total amount spent = 3*5000 = 15000.

                Average = 15000/(191875/91)
                              = 7.11.


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