A+2A+3A+.+49A+50A+50B+49B+.+2B+B

问题描述:

A+2A+3A+.+49A+50A+50B+49B+.+2B+B

A+2A+3A+.+49A+50A+50B+49B+.+2B+B
= [(1+50)*50/2] *(A+B)
= 1275(A+B)