Average

9.Of Five numbers, whose average is 60, the first is one-fourth of the sum of the last three. The first number is : A)36 B)37 C)39 D)40 Answer : Option D Explanation: Let the first number be x, Then, sum of the four numbers = x + 5x = 6x. so, 6x/4 = 60 or x = (60 * 4) / 6 = 40. 10.The average of five numbers is 25. If one number is excluded, the average becomes 20. The excluded number is : A)44 B)45 C)48 D)47 Answer : Option B Explanation: Excluded number = (25 x 5) - (20 x 4) = 125 - 80 = 45. 11. A motorist travels to a place 150 km away at an average speed of 50 km/hr and returns at 30 km/hr. His average speed for the whole journey in km/hr is : A)36 B)37 C)37.5 D)38 Answer : Option C Explanation: Average speed = (2xy) /(x + y) km/hr = (2 * 50 * 30) / (50 + 30) km/hr. 37.5 km/hr. 12.The average age of the boys in a class is 16 years and that of the girls is 15 years. The average age for the whole class is : A)15 B)25 C)35 D)Data Inadequate Answer : Option A Explanation: Clearly, to find the average, we ought to know the number of boys, girls or students in the class, neither of which has been given. So, the data provided is inadequate.

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