Question

the average of 15 numbers is 7. angelo is adding these numbers and mistakenly reads 6 of the numbers as 9 instead of seven, what average will he get?

Answer 1

if the average of 15 numbers is 7, the sum should be
`15*7=105`
if for 6 of the numbers, he sees 9 instead of 7, he is counting 2 additional units per number, so his sum will be greater by
`2*6=12`, therefore the sum he gets is
`105+12=117`
from that, the average he calculates is
`(117)/(15) = 7.8`