Question

The mean of six numbers is 10. When

mother number is added the new mean is
9. Find the number added.​

Answer 1

3

Explanation:

If 6 numbers have a mean value of 10, it means that the sum of the numbers divided 6 is equal to 10. This can be expressed as:

x÷6=10

x=60

The new number added will be the 7th number and now the mean is 9. You have to ask what number divided by 7 is equal to 9? This can be expressed as:

y÷7=9

y=63

63-60=3

So the new number added is 3

Answer 2

3

Explanation:

Mean is calculated as

mean =
`(sum)/(count)`

Given the mean of 6 numbers is 10, then

`(sum)/(6)` = 10 ( multiply both sides by 6 )

sum = 60

When another number x is added then count is 7

`(60+x)/(7)` = 9 ( multiply both sides by 7 )

60 + x = 63 ( subtract 60 from both sides )

x = 3 ← the number added