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__Averages Formulae__

1. Average

Average = (Sum of observations/Number of observations)

2. Average Speed

Suppose a man covers a certain distance at X kmph and an equal distance at Y kmph.

Then, the average speed during the whole journey is {2xy/(x+y)} kmph.

Average = (Sum of observations/Number of observations)

2. Average Speed

Suppose a man covers a certain distance at X kmph and an equal distance at Y kmph.

Then, the average speed during the whole journey is {2xy/(x+y)} kmph.

6. The average of first 10 prime numbers is?
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Answer: Option C

Explanation:

Sum of 10 prime no. = 129

Average = 129/10 = 12.9

7. The average age of three boys is 15 years and their ages are in proportion 3:5:7. What is the age in years of the youngest boy?
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8. The average of 1^{st} 3 of 4 numbers is 16 and of the last 3 are 15. If the sum of the first and the last number is 13. What is the last numbers?
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Answer: Option C

Explanation:

A + B + C = 48

B + C + D = 45

A + D = 13

A “ D = 3

A + D = 13

2D = 10

D = 5

9. The average of 9 observations was 9, that of the 1^{st} of 5 being 10 and that of the last 5 being 8. What was the 5^{th} observation?
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Answer: Option A

Explanation:

1 to 9 = 9 * 9 = 81

1 to 5 = 5 * 10 = 50

5 to 9 = 5 * 8 = 40

5^{th} = 50 + 40 = 90 “ 81 =
9

10. The average of 10 numbers is calculated as 15. It is discovered later on that while calculating the average, one number namely 36 was wrongly read as 26. The correct average is?
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