Question

1/20+1/30+1/42+1/56+1/72+1/90 = ?

Answer 1

1/20+1/30+1/42+1/56+1/72+1/90 = 3/20

Answer 2

1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90

= 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9 + 1/9.10

= 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8 + 1/8 - 1/9 + 1/9 - 1/10

= 1/4 - 1/10

= 3/20