Question

The average of 7 numbers is 30. The average of first three of them is 23 and last three of them is 42. Fourth number is?

Answer 1

Step-by-step explanation:

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Answer 2

The fourth number is 15

Step-by-step explanation:

$Average = \frac{\text{Sum of all observations}}{\text{No. of observations}}$

The average of 7 numbers is 30.

So, $30 = \frac{\text{Sum of 7 numbers}}{7}$

$30 \times 7 = \text{Sum of 7 numbers}$

$210= \text{Sum of 7 numbers}$

The average of first three of them is 23

So, $23 = \frac{\text{Sum of first 3 numbers}}{3}$

$23 \times 3 = \text{Sum of first 3 numbers}$

$69= \text{Sum of first 3 numbers}$

The average of three of them is 42.

$42 = \frac{\text{Sum of last 3 numbers}}{3}$

$42 \times 3 = \text{Sum of last 3 numbers}$

$126= \text{Sum of last 3 numbers}$

Fourth number = Sum of 7 numbers - (Sum of first 3 numbers + Sum of last three numbers)

Fourth number = 210-(69+126)=15

Hence The fourth number is 15

#Learn more:

Find the average of 12 number if first 8numbers average is 21 find the average of last 4 numbers

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