Question

10乘11分之3加11乘12分之3加12乘13分之3……19乘20分之3,这道题有什么规律?

Answer 1

=3×(1/10×11+1/11×12+……+1/19×20)

=3×(1/10-1/11+1/11-1/12+……+1/19-1/20)

=3×(1/10-1/20)

=3/20