Let a and b be the two numbers so that a+b136, given (1)
Let 2n (even) means be inserted between them whose sum =(2n+1) given ...(2)
Now we know that in an A.P., sum of 2n means =2n×(singleA.M,) or 2n+1=2n(a+b2) by (2) or 2n+1=n.136, by (1) or 12n+6=13n,∴n=6.
Hence the number of means inserted =2n=12.