1/2*7+1/7*12+1/12*17+1/17*22+……+1/92*97+1/97*102
=1/5(1/2-1/7)+1/5(1/7-1/12)+...+1/5(1/92-1/97)+1/5(1/97-1/102)
=1/5(1/2-1/7+1/7-1/12+...+1/92-1/97+1/97-1/102)
=1/5(1/2-1/102)
=1/5*50/102
=10/102
=5/51