Simple mathematical calculation 1 / 2 * 3 + 1 / 3 * 4 + 1 / 4 * 5 +... 1 / 99 * 100

Original formula = 1 / 2-1 / 3 + 1 / 3-1 / 4 -1/99+1/99-1/100=49/100
Note: 1 / 2 × 3 = 1 / 2-1 / 3 do not believe you try
The general case 1 / N (n + 1) = 1 / N - 1 / (n + 1) can be proved
But if it is a primary school, we can only find the above rules

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