Ten scores have a mean of 9. What must the 11th score be to increase the mean by 1?

Question

Ten scores have a mean of 9. What must the 11th score be to increase the mean by 1?

Answer 1

(The sum of the ten scores)/10 = 9

 

multiply each side by 10

 

the sum of the ten scores = 90

 

Now add a number to the sum of the ten scores, divided by the number 11 and that will result in a new mean of 10

 

(90 + x)/11 = 10

 

90 + x = 110

 

x = 20

 

the 11th score would be 20