Question

口算 5 9 ×15=	3 5 ×2=	1 4 × 4 5 =	1 9 × 3 7 =	7 12 × 3 4 =
1× 3 20 =	2 5 × 15 4 =	4 17 ×34=	8 21 × 7 16 =	1 20 × 2 3 =
5 6 × 2 15 =	15 17 × 17 15 =	3 4 × 1 5 =	6 11 × 1 12 =	3 22 × 11 13 =
7 6 ×24=	4 7 × 3 8 =	13 15 ×30=	28× 7 24 =	5 6 × 3 7 =

Answer 1

分析：此题分为两种类型：一种是分数与整数相乘，把分子与整数相乘的积做分子，分母不变，能约分的要约分；一种是分数与分数相乘，把分子相乘的积做分子，分母相乘的积做分母，能约分的要约分．

解答：解：

5

9

×15=

25

3

；        

3

5

×2=

6

5

；          

1

4

×

4

5

=

1

5

；         

1

9

×

3

7

=

1

21

；          

7

12

×

3

4

=

7

16

；
1×

3

20

=

3

20

；            

2

5

×

15

4

=

3

2

；         

4

17

×34=8；         

8

21

×

7

16

=

1

6

；         

1

20

×

2

3

=

1

30

；

5

6

×

2

15

=

1

9

；           

15

17

×

17

15

=1；        

3

4

×

1

5

=

3

20

；        

6

11

×

1

12

=

1

22

；        

3

22

×

11

13

=

3

26

；

7

6

×24=28；            

4

7

×

3

8

=

3

14

；        

13

15

×30=26；        28×

7

24

=

49

6

；        

5

6

×

3

7

=

5

14

；

点评：此题考查了分数乘法的计算，掌握方法，注意约分．