Question

the mean of 20 observations is 12•5.by error one observation was noted as _15 instead of 15 the correct mean is

Answer 1

given
incorrect mean=12.5
no. of observation
mean = sum of observation /no. of observation
thus incorrect sum of observation will be

20*12.5 =250

since one observarion noted as -15 instead of 15
thus
correct sum =incorrect sum -(-15)+15 =250+15+15=280

correct mean = correct sum / no. of observation

=280/20=14
thus correct mean =14

Answer 2

Hey buddy..

Have a look at the picture..
Hope it's helpful for you...

Stay blessed