楼主
2楼
第一道写成这样就比较容易看的出来:
[(1+1/2+1/3+1/4)+1/5]*(1/2+1/3+1/4+1/5))-(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)
=(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)+1/5*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)
=1/5*(1/2+1/3+1/4+1/5)
应该明白了吧!
[(1+1/2+1/3+1/4)+1/5]*(1/2+1/3+1/4+1/5))-(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)
=(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)+1/5*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)
=1/5*(1/2+1/3+1/4+1/5)
应该明白了吧!
3楼
1/(1/10-1/15)=30
4楼
(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)
对这个分析,(1/2+1/3+1/4+1/5)这个是相同的所以可以把这个提出来.
(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)
=(1/2+1/3+1/4+1/5)*[(1+1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)]
=(1+1/2+1/3+1/4+1/5)*1/5
=1/5+1/10+1/15+1
=41/30
对这个分析,(1/2+1/3+1/4+1/5)这个是相同的所以可以把这个提出来.
(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)
=(1/2+1/3+1/4+1/5)*[(1+1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)]
=(1+1/2+1/3+1/4+1/5)*1/5
=1/5+1/10+1/15+1
=41/30
5楼
还有一道题:一个蓄水池开单开进水管10小时可以放满一池水,单开排水管要15小时可以排完,如果二管同时开,要几小时才可以放满一池水?
分析:进水工作效率为1/10.排水管工作效率为1/15.他们同时打开每小时放进池的水为1/10-1/15. 列式为1/(1/10-1/15)=30(小时).
分析:进水工作效率为1/10.排水管工作效率为1/15.他们同时打开每小时放进池的水为1/10-1/15. 列式为1/(1/10-1/15)=30(小时).
6楼
自己多观察!
做时心要静,莫慌!
做时心要静,莫慌!
7楼
(1+1/2+1/3+1/4+1/5)#(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)#(1/2+1/3+1/4+1/5) =(1/5)#(1/2+1/3+1/4+1/5)
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