Question

4.2.×99+42的简便方法？

Answer 1

4.2×99+42
=4.2*100-4.2+42
=420+42-4.2
=462-4.2
=457.8

Answer 2

4.2×99+42
=4.2×（100-1）+42
=420-4.2+42
=457.8

Answer 3

4.2*（100-1）+42
=4.2*100-4.2+42
=42-4.2+42
=79.8

Answer 4

原式=42×（99+1）
=42×100
=4200

Answer 5

4.2x（100-1）+42
=42-4.2+42
=84-4.2
=79.8