Analysis: This question adopts the law of addition and exchange, and is calculated after rounding. The steps are as follows:

24.6-3.98+5.4-6.02

=(24.6+5.4)-(3.98+6.02)

=30- 10

=20

2、27× 17/26

Analysis: This problem first converts 27 into (26+ 1) by using the law of additive distribution, and then makes the operation simple by using the law of multiplicative association.

27× 17/26

=(26+ 1)× 17/26

=26× 17/26+ 1× 17/26

= 17+ 17/26

= 17 and 17/26

3、528-99

Analysis: Use rounding method and subtraction combination method to calculate. First, 99 is converted into (100- 1) by rounding method, and then a-b-c=a-(b+c) is used for simple calculation. The steps are as follows:

528-99

=528-( 100- 1)

=528- 100+ 1

=428+ 1

=429

4、 1.2×2.5+0.8×2.5

Analysis: Using the method of extracting the common factor, the formula: ac+ab=a(b+c), extracting the common factor of 2.5, 1.2, 0.8, and adding them together just makes the operation simple.

1.2×2.5+0.8×2.5

=( 1.2+0.8)×2.5

=2×2.5

=5?

5、2.96×40

Analysis: Firstly, the problem is transformed from 2.96×40 to 29.6x4 by using the law of multiplicative distribution, and then a simple calculation is made by using the law of multiplicative association.

2.96×40

=29.6x4

=(30-0.4)x4

=30×4+0.4×4

= 120- 1.6

= 1 18.4

6、0.36 x 1.5 - 0.45？

Analysis: In this question, 0.45 is converted into 1.5 x 0.3 by multiplication and division, and then the common factor of 1.5 can be extracted, and then it can be simply calculated according to the multiplication and division method and the associative law.

0.36 x 1.5 - 0.45？

= 0.36 x 1.5 - 1.5 x 0.3？

=? 1.5 × (0.36 - 0.3)?

=? 1.5 × 0.06?

= 0.09

7、46×44/45

Analysis: In this question, 46 is converted into (45+ 1) by using the law of additive distribution, and then the operation is simple by using the law of multiplicative association: (a×b)×c=a×(b×c).

46×44/45

=(45+ 1)×44/45

=45×44/45+44/45

=44+44/45

=44 and 44/45

8、 1.6×7.5× 1.25

Analysis: In this question, 1.6 is converted into 2×0.8 by the law of multiplicative distribution, and then rounded up by the law of multiplicative association: (a×b)×c=a×(b×c) for simple calculation.

1.6×7.5× 1.25

=2×0.8×7.5× 1.25

=(2×7.5)×(0.8× 1.25)

= 15× 1

= 15

9、0.72× 10. 1

Analysis: Firstly, this problem transforms 10. 1 into 10+0. 1 by using the law of addition and distribution, and then the operation is simple.

0.72× 10. 1

=0.72×( 10+0. 1)

=0.72× 10+0.72×0. 1

=7.2+0.072

=7.272