Question

布里奇特在杂货店买了一袋苹果。她把一半苹果给了安。然后她给了凯茜 $3$ 个苹果，自己留下 $4$ 个苹果。布里奇特买了多少个苹果？

Bridget bought a bag of apples at the grocery store. She gave half of the apples to Ann. Then she gave Cassie $3$ apples, keeping $4$ apples for herself. How many apples did Bridget buy?

$3$

$4$

$7$

$11$

$14$

答案：E

知识点：逆推法

难度评级：370

小提示：

从布里奇特自己留下和给凯茜的苹果数倒推

Work backward from the apples Bridget kept and gave to Cassie.

大提示：

这些苹果就是没有给安的那一半

Those apples were the half not given to Ann.

解答：

可以倒推，从布里奇特自己留下的 $4$ 个苹果开始。加上她给凯茜的 $3$ 个苹果，这一半共有 $7$ 个苹果。

因为她把原来苹果的一半给了安，所以再乘以 $2$ 。 $7 \cdot 2 = 14$ ，因此布里奇特一开始有 $14$ 个苹果。

所以正确答案是 E。

We can work backwards, starting with the $4$ apples that Bridget kept for herself. Adding the $3$ apples that she gave Cassie, she now has $7$ apples.

Finally, we multiply this value by $2$ since she gave half of her initial apples to Ann. $7 \cdot 2 = 14,$ so Bridget started off with $14$ apples.

Thus, E is the correct answer.

2009 AMC 8 第 1 题

答案：E

难度评级：370

小提示：

大提示：

解答：

其他年份的第 1 题