The average of $6$ observations is $12 .$ A new seventh observation is included and the new average is decreased by $1$. The seventh observation is
$1$
$3$
$5$
$6$
Of the three numbers, the average of the first and the second is greater than the average of the second and the third by $15 .$ What is the difference between the first and the third of the three numbers?
The average of six numbers is $20 .$ If one number is removed, the average becomes $15 .$ What is the number removed ?
What is the average of first $7$ multiples of $7\, ?$
A batsman score $98$ runs in the $17^{\text {th }}$ match of his career. His average runs per match increase by $2.5$ What is his average before the $17^{\text {th }}$ match?
Average rainfall on Monday, Tuesday, Wednesday and Thursday is $420.5\, cm$ and average on Tuesday, Wednesday, Thursday and Friday is $440.5\, cm .$ If the ratio of rainfall for Monday and Friday is $20: 21,$ find the rainfall in $cm$ on Monday and Friday.