Question

66*21+19*21+85*19这个题用简便方法怎么做?

Answer 1

66*21+19*21+85*19
=21*（66+19）+85*19
=21*85+85*19
=85*（21+19）
=85*40
=3400
通过观察，先把前两组（66*21+19*21）利用反向的乘法分配律进行计算得出（21*85）在与后面一组（85*19）再进行反向的乘法分配律就算就可以了
反向的乘法分配律：a*c+b*c=(a+b)*c

Answer 2

66*21+19*21+85*19
= (66+19)*21+85*19
= 85*21+85*19
= 85*(21+19)
= 85*40
= 3400

Answer 3

=66*21+4*21+15*21+85*19
=66*21+4*21+15*19+15*2+85*19
=(66+4)*21+(85+15)*19+15*2
=1470+1900+30
=3400

Answer 4

66*21+19*21+85*19
= (66+19)*21+85*19
= 85*21+85*19
= 85*(21+19)
= 85*40
= 3400

Answer 5

66*21+19*21+85*19
= (66+19)*21+85*19
= 85*21+85*19
= 85*(21+19)
= 85*40
= 3400