Question

下列哪一组三个数的和不等于 $1$ ？

Which triplet of numbers has a sum NOT equal to $1?$

$(\frac12,\frac13,\frac16)$

$(2,-2,1)$

$(0.1,0.3,0.6)$

$(1.1,-2.1,1.0)$

$(-\frac32,-\frac52,5)$

知识点：分数小数

A 等于 $\dfrac{3}{6} + \dfrac{2}{6} + \dfrac{1}{6} = 1.$

B 化简为 $2 - 2 + 1 = 1.$

C 的和是 $.1 + .3 + .6 = 1.$

但 D 的和为 $1.1 - 2.1 + 1.0 = 0.$

为确认起见，E 的和为 $-\dfrac{8}{2} + 5 = 5 - 4 = 1.$

所以正确答案是 D。

We have that A is the same as $\dfrac{3}{6} + \dfrac{2}{6} + \dfrac{1}{6} = 1.$

B reduces to $2 - 2 + 1 = 1.$

C adds up to $.1 + .3 + .6 = 1.$

D however adds to $1.1 - 2.1 + 1.0 = 0.$

To make sure, we check that E has a sum of $-\dfrac{8}{2} + 5 = 5 - 4 = 1.$

Thus, D is the correct answer.