What is 1 / 2 × 1 / 5 + 1 / 5 × 1 / 8 +. + 1 / 17 × 1 / 20?

What is 1 / 2 × 1 / 5 + 1 / 5 × 1 / 8 +. + 1 / 17 × 1 / 20?

1 / 2 × 5 / 1 + 1 / 5 × 8 / 1 +. + 1 / 17 × 20 / 1
=1/3×[(1/2-1/5)+(1/5-1/8)+…… +(1/17-1/20)]
=1/3×(1/2-1/5+1/5-1/8+…… +1/17-1/20)
=1/3*(1/2-1/20)
=1/3*9/20
=3/20

Simple calculation of 3 / 23 times 70

=3/23 X (69+1)
=3/23 X69 +3/23 X1
=9+3/23
=9 and 3 / 23
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How to simply calculate 61.3 times 0.15 + 15 times 1.387

61.3 times 0.15 + 15 times 1.387
=0.613*15+15*1.387
=15*(0.613+1.387)
=15*2
=30

Simple calculation of 63 times 62 / 61
It's too late

63*(61+1)/61
=(63*61+63)/61
=(63*61+61+2)/61
=64+2/61