Tính A = 5/2.4 5/4/6 5/6.8 ... 5/48.50

A = 52.4+54.6+....+548.50

A = 512.4+14.6+....+148.50

A =  5222.4+24.6+....+248.50

A = 5212−14+14−16+...+148−150

A = 5212−150

A = 52.1225=65.