1、24.6-3.98/ 1+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