第 12 条 · 连续相减

Sometimes also we may have several numbers to subtract from a single one; as, for instance, 50 - 1 - 3 - 5 - 7 - 9.

有时，我们也可能要从一个数里连续减去几个数。例如：50 - 1 - 3 - 5 - 7 - 9。

This signifies, first, take 1 from 50, and there remain 49; take 3 from that remainder, and there will remain 46; take away 5, and 41 remain; take away 7, and 34 remain; lastly, from that take 9, and there remain 25.

这表示：先从 50 中取走 1，剩 49；再从这个余数中取走 3，剩 46；取走 5，剩 41；取走 7，剩 34；最后再取走 9，剩 25。

But as the numbers 1, 3, 5, 7, 9, are all to be subtracted, it is the same thing if we subtract their sum, which is 25, at once from 50, and the remainder will be 25 as before.

不过，因为 1、3、5、7、9 都要被减去，所以也可以先求它们的和 25，再一次从 50 中减去；余数仍然是 25。