The average of x number is y and average of y numbers is x. Then the average of all the numbers taken together is
(x+y)/2xy
2xy/(x+y)
(x^{2}+y^{2})/(x+y)
xy/(x+y)
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#  Quiz 

1
Discuss

Find the average of all prime numbers between 30 and 50.
Solution 
2
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Average of a, b, and c is 11; average of c, d and e is 17; average of e and f is 22 and average of e and c is 17. Find out the average of a, b, c, d, e and f.
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3
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If the mean of 4 observations is 20, when a constant 'c' is added to each observation, the mean becomes 22. The value of c is :
Solution 
4
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The average monthly income of P and Q is Rs. 6000; that of Q and R is Rs. 5250; and that P and R is Rs. 5500. What is P’s monthly income?
Solution 
5
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The average height of 30 boys out of a class of 50 is 160 cm. If the average height of the remaining boys is 165 cm, the average height of the whole class (in cm) is :
Solution 
6
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The average age of P, Q and R is 15 years more than R's age. If the total age of P and Q together is 39 years, then R's age is ?
Solution 
7
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When the average age of a couple and their son was 42 years, the son married and got a child after one year. When the child was 5 years old, the average age of the family became 36 years. What was the age of daughterin law at the time of their marriage ?
Solution 
8
Discuss

The mean weight of 100 students in a class is 46 kg. The mean weight of boys is 50 and of girls is 40 kg. Therefore, the number of boys is:
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9
Discuss

A student finds the average of 10, 2 digits numbers. If the digits of one of the numbers interchanged, the average increases by 3.6. The difference between the digits of the 2 digits number is :
Solution 
10
Discuss

The average age of four boys A, B, C and D is 5 years and the average age A, B, D, E is 6 years. C is 8 years old. The age of E is (in years) :
Solution 
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