4.9╳10.2用简便

Question

4.9╳10.2用简便

Answer 1

4.9╳10.2
＝4.9╳10＋4.9╳0.2
＝49＋（5－0.1）╳0.2
＝49＋1－0.02
＝49.98

Answer 2

4.9x10.2
＝4.9x（10＋0.2）
＝4.9x10＋4.9x0.2
＝49＋0.98
＝49.98

Answer 3

4.9╳10.2

=4.9*（10+0.2）
=4.9*10+4.9*0.2
=49+0.98
=49.98

Answer 4

4.9*10.2
= 4.9*5.1*2
=（5-0.1）（5+0.1）*2
=（5^2-0.1^2）*2
=50 - 0.02

= 49.98