数学题简算(分数)1/4*37+0.75*21(1/30+1/35+1/63)*2又1/718*6/7+6*1/7+16/7*61880*199又9/10-1999*187又9/1039*148/149+148*86/149+48*74/1492004除以2004又2004/200651又2/3*3/5+71又3/4*4/7+91又4/5*5/91998+1989*1987/1988*1989-11/1*2=1-1/2,1/
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数学题简算(分数)1/4*37+0.75*21(1/30+1/35+1/63)*2又1/718*6/7+6*1/7+16/7*61880*199又9/10-1999*187又9/1039*148/149+148*86/149+48*74/1492004除以2004又2004/200651又2/3*3/5+71又3/4*4/7+91又4/5*5/91998+1989*1987/1988*1989-11/1*2=1-1/2,1/
数学题简算(分数)
1/4*37+0.75*21
(1/30+1/35+1/63)*2又1/7
18*6/7+6*1/7+16/7*6
1880*199又9/10-1999*187又9/10
39*148/149+148*86/149+48*74/149
2004除以2004又2004/2006
51又2/3*3/5+71又3/4*4/7+91又4/5*5/9
1998+1989*1987/1988*1989-1
1/1*2=1-1/2,1/2*3=1/2-1/3,1/3*4=1/3-1/4,1/4*5=()-(),1/5*6=()-().1/n*(n+1)()-();利用上面的规律计算:
1/1*2+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7
说明道理+列式
数学题简算(分数)1/4*37+0.75*21(1/30+1/35+1/63)*2又1/718*6/7+6*1/7+16/7*61880*199又9/10-1999*187又9/1039*148/149+148*86/149+48*74/1492004除以2004又2004/200651又2/3*3/5+71又3/4*4/7+91又4/5*5/91998+1989*1987/1988*1989-11/1*2=1-1/2,1/
1/4*37+0.75*21
= 37/4 + 3/4 * 21
= 37/4 + 21*3 /4
= 37/4 + 63/4
= 100/4
= 25
(1/30+1/35+1/63)*2又1/7
= (1/5*6 + 1/5*7 + 1/7*9 ) * 15/7
= ( 1/5-1/6 + 2/5-2/7 + 2/7-2/9) * 15/7
= ( 3/5 - 1/6 - 2/9 )* 15/7
= (54/90 - 15/90 - 20/90)*15/7
= 19/90 * 15/7
= 19/42
18*6/7+6*1/7+16/7*6
=(18+1+16)*6/7
= 35*6/7
= 5*6
= 30
1880*199又9/10-1999*187又9/10
= 1880 * 1999/10 - 1999 * 1879/10
= (1880-1879)*1999/10
= 1*1999/10
= 1999/10
= 199又9/10
39*148/149+148*86/149+48*74/149
= 39* 148/149 + 86* 148/149 + 24* 148/149
=(39+86+24) *148/149
= 149 * 148/149
= 148
2004除以2004又2004/2006
= 2004 ÷ (2004*2006 + 2004)/2006
= 2004 × 2006/(2004 * 2007)
= 2006/2007
51又2/3*3/5+71又3/4*4/7+91又4/5*5/9
= 155/5 + 287/7 + 459/9
= 31 + 41 + 51
= 123
1988+1989*1987/1988*1989-1
= (1988+1989*1987)/(1987*1989+1989-1)
= (1988+1989*1987)/(1987*1989+1988)
= 1
1/1*2=1-1/2,1/2*3=1/2-1/3,1/3*4=1/3-1/4,1/4*5=()-(),1/5*6=()-().1/n*(n+1)()-();
1/4*5 = 1/5 - 1/6 ; 1/5*6 = 1/5 - 1/6 ;
1/n*(n+1) = 1/ n - 1/(n+1)
利用上面的规律计算:
1/1*2+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7
= 1- 1/2+ 1/2- 1/3+ 1/3- 1/4+ 1/4- 1/5+ 1/5- 1/6+ 1/6- 1/7
= 1 - 1/7
= 6/7