1、24.6-3.98+5.4-6.02

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. The steps are as follows:

27× 17/26

=(26+ 1)× 17/26

=26× 17/26+ 1× 17/26

= 17+ 17/26

= 17 and 17/26

Simple calculation method:

1. In the operation at the same level, the positions of numbers can be exchanged at will, but they should be exchanged with the previous symbols. (addition or multiplication commutative law)

2. In the operation at the same level, parentheses can be added or deleted directly after the plus sign or multiplication sign; Add brackets after minus sign and division sign, delete brackets, and change the symbols in brackets. (law of addition or multiplication)

3. Make up one method, make up ten methods, make up a hundred methods, and make up a thousand methods: "Make up nine before, make up ten after".

Be sure to remember: 25 replace 4 with 100, 125 replace 8 with 1000 (rounding idea).