简便运算,越简便越好9+19+29+39+49+59+69+79+89+99

问题描述:

简便运算,越简便越好9+19+29+39+49+59+69+79+89+99

10*10-10

=10+20+30+40+50+60+70+80+90+100-10
=110*5-10
=540
10^55-10=540

9+19+29+39+49+59+69+79+89+99
=9*10+90*(10/2)=540

(10+20+30+40+50+60+70+80+90+100)-10

你可以发现9+99=19+89=……=49+59=108
所以原式=9+19+29+39+49+59+69+79+89+99
=108×5
=540