Question

Mean of 7 numbers is 20. If one of the number is added to the list, their mean is 21. Find the added number.

Answer 1

Answer:

let the added number be x.

According to the question

$mean \: of \: seven \: numbers = 20$

$sum \: of \: seven \: numbers = 20 \times 7 = 140$

$after \: adding \: x$

$sum \: of \: eight \: numbers = 140 + x$

$mean \: of \: eight \: numbers = \frac{140 + x}{8}$

$\frac{140 + x}{8} = 21$

$140 + x = 21 \times 8 = 168$

$x = 168 - 140 = 28$

$so \: the \: added \: number \: is \: 28$