1. 把下面的条件改写成数量关系式。
例:实际比原计划多做20个。
实际做的个数-原计划做的个数=20个
(1)实际比原计划提前5天完成任务。

(2)实际比原计划减少了10人。

(1)原计划完成任务的天数 - 实际完成任务的天数 = 5天；(2)原计划的人数 - 实际的人数 = 10人

改写数量关系式时，需明确两个比较量及相差量，用“较大量 - 较小量 = 相差量”的形式表示。

2. 用2,2,4,8这四个数,通过+、-、×、÷四则运算,列成得数是24的算式,你能列出几个？

能列出4个，分别是$2×2×4 +8=24$、$8×4 -2×2=24$、$8×(4 -2÷2)=24$、$4×(8÷2 +2)=24$

根据四则混合运算规则，用2、2、4、8四个数各一次，通过加、减、乘、除运算组合得到24，符合要求的算式如下：
1. $2×2×4 + 8 = 24$
2. $8×4 - 2×2 = 24$
3. $8×(4 - 2÷2) = 24$
4. $4×(8÷2 + 2) = 24$

第15页第2题答案：

第15页“数字谜语”答案：
七上八下、百里挑一、
一分为二、不三不四。
阅读短文,回答问题。Read and answer the questions.
Jack and Simon are Chinese boys. They live in England. They are brothers. They look the same. Jack is eleven. Simon is eleven, too. They are in Class Two, Grade Four. Jack studies harder than Simon. Today is their birthday. There is a big cake on the table. Their parents sit between them. There are two nice gifts for them. The basketball is for Simon, and the new book is for Jack. They like the gifts very much.
(1) Are Jack and Simon twins(双胞胎)?

(2) Where do they live?

(3) Which class are they in?

(4) Is there a cake on the table?

(5) Which gift is for Simon?


玩

(1) Yes, they are. (2) They live in England. (3) They are in Class Two, Grade Four. (4) Yes, there is. (5) The basketball is for Simon.

根据短文内容，逐一对应问题信息：1. 由“They look the same. Jack is eleven. Simon is eleven, too.”可知Jack和Simon是双胞胎；2. 由“They live in England.”可知他们的居住地点；3. 由“They are in Class Two, Grade Four.”可知他们所在班级；4. 由“There is a big cake on the table.”可知桌子上有蛋糕；5. 由“The basketball is for Simon”可知给Simon的礼物。