Question

求和

$\dfrac12 + \dfrac13 + \dfrac14 + \dfrac15 + \dfrac16 + \dfrac17,$

时，使用的最小公分母是多少？

When finding the sum

$\dfrac12 + \dfrac13 + \dfrac14 + \dfrac15 + \dfrac16 + \dfrac17,$

what is the least common denominator used?

$120$

$210$

$420$

$840$

$5040$

最小公倍数必须包含 $4 = 2^2$ 、 $3$ 、 $5$ 和 $7$ （因数 $6 = 2 \times 3$ 已经被覆盖）。

所以它是 $4 \times 3 \times 5 \times 7 = 420$ 。

所以正确答案是 C。

The least common multiple must include $4 = 2^2,$ $3,$ $5,$ and $7$ (the factor $6 = 2 \times 3$ is already covered).

So it is $4 \times 3 \times 5 \times 7 = 420.$

Thus, the correct answer is C .