1、24.6-3.98+5.4-6.02

Analysis: This question adopts the law of addition and exchange, and is calculated after rounding.

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.

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