数学课课练答案56页等你挑战的答案（题：5乘8分之1+8乘11分之1+.+98乘101分之1巧算

1/(5×8)+1/(8×11)+........+1/(98×101)
=1/3 ×(1/5-1/8)+1/3×(1/8-1/11)...+1/3×(1/98-1/101)
=1/3×（1/5-1/8+1/8-1/11+...+1/98-1/101）
=1/3×(1/5-1/101)
=1/3×96/505
=32/505

=1/3*(1/5-1/8)+1/3*(1/8-1/11)...+1/3*(1/98-1/101)=1/3(1/5-1/101)=32/505