Question 979715
The mean of 12 numbers is 18.
 If each of the first 6 numbers is increased by 2 and each of the remaining numbers is also increased by 4,
 obtain the new mean of the 12 numbers.
:
initially the average can be written
{{{12(18)/12}}} which is 18 obviously
:
add 2 to the 1st 6 values of 18 and 4 to last 6 values of 18
A = {{{((6*20) + (6*22))/12}}} 
A = {{{(120 + 132)/12}}}
A = 252/12
A =  21 is the new mean