Question

the average of 7 numbers 128. find the seventh number if the other six are 127, 133, 118, 129, 122 and 139.

Answer 1

average=mean=sum of all/no.of all
let the 7th no. be x
128=127+133+118+129+122+139+x/7
128×7=768+x
896-768=x=128







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Answer 2

since, the average of seven numbers is 128.
so, the sum of the 7 numbers =7×128
=896
now, the sum of six numbers is 127+133+118+129+122+139=768
hence, the 7th number =896-768
=128
thanks