Calculation: (1-2) × (2-3) × (3-4) × ×（19－20） Process!

Each bracket is - 1
The first number in brackets is 1 to 19
So there are 19 brackets
19 is odd
Odd number - 1 multiplication
So the original formula = - 1

Simple calculation 1 / 1 * 2 + 1 / 2 * 3 + 1 / 3 * 4 + 1 / 4 * 5 + 1 / 5 * 6 +1/19*20=

(1-1/2)+(1/2-1/3).-1/19)+(1/19-1/20)=1-1/20=19/20
Tip: split the score, for example: 1 / 2 * 3 = 1 / 2-1 / 3

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