Question

22. The average of 3 numbers is 20 and that of the first
two is 25. Find the third number.
(a) 15
(b) 10
(c) 20
(d) 12
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Answer 1

Step-by-step explanation:

the third one is 15

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Answer 2

Answer:

option (b) 10

Step-by-step explanation:

Given :

The average of 3 numbers is 20 and that of the first  two is 25.

To find :

the third number

Solution :

We know,

Average = Sum of observations/number of observations

Let the three numbers be x, y and z

Average of the first two numbers = 25

x + y/2 = 25

x + y = 25(2)

x + y = 50 --[1]

Average of the three numbers = 20

x + y + z/3 = 20

x + y + z = 20(3)

x + y + z = 60

50 + z = 60  ( ∵ eq. [1] )

z = 60 - 50

z = 10

Therefore, the third number is 10