Bài 25: Tính
3/2 + 4/5 _ 7/10 3/2 X 4/5 X 7/9
3/4 + 6/5 - 9/10 8/1 - 4/5 - 2/85
7 - ( 4/8 + 5/6 ) 3/2 x 4/5 x 7/9
2/5 x 5/4 x 9/7 6/7 : 5/6 : 3/2
( 3/2 + 7/5 ) x 3/4
Bài 26: Tính bằng cách thuận tiện nhất
1/5 x 4/7 + 1/5 x 3/7 - 1/5 3/7 x 5/8 +3/7 x 11/8
6/13 - 12/5 + 7/13 + 17/5 5/8 + 14/18 - 3/8 + 2/9 +14/8
Lưu ý: *Trình bày rõ cách tính*
Bài `25` :
`3/2 + 4/5 _ 7/10` Xem lại đề
___________________________
`3/4 + 6/5 - 9/10`
`=15/2+ 24/20 - 18/20`
`=(15 +24-18)/20`
`=21/20`
_____________________________
`7 - ( 4/8 + 5/6 )`
`=7 - (1/2 + 5/6)`
`=7 - (3/6 + 5/6)`
`=7 - 4/3`
`=21/3 - 4/3`
`=(21-4)/3`
`=18/3`
`=6`
_________________________
`2/5 xx 5/4 xx 9/7`
`=(2xx5xx9)/(5xx4xx7)`
`=(1xx1xx9)/(1xx2xx7)`
`=9/14`
_______________________________
`( 3/2 + 7/5 ) xx 3/4`
`=(15/10 + 14/10) xx 3/4`
`=((15+14)/10) xx 3/4`
`=29/10 xx 3/4`
`=87/40`
_____________________________
`3/2 xx 4/5 xx 7/9`
`=(3xx4xx7)/(2xx5xx9)`
`=84/90`
`=14/15`
______________________________
`8/1 - 4/5 - 2/85`
`=680/85 - 68/85 - 2/85`
`=(680 - 68 -2)/85`
`=610/85`
`=122/17`
___________________________
`3/2 xx 4/5 xx 7/9`
`=(3xx4xx7)/(2xx5xx9)`
`=84/90`
`=14/15`
______________________________________
`6/7 : 5/6 : 3/2`
`=6/7 xx 6/5 xx 2/3`
`=(6xx6xx2)/(7xx5xx3)`
`=72/105`
`=24/35`
________________________________________
Bài `26` :
`1/5 xx 4/7 + 1/5 xx 3/7 - 1/5`
`=1/5 xx 4/7 + 1/5 xx 3/7 - 1/5xx1`
`=1/5 xx ( 4/7 + 3/7 - 1)`
`=1/5 xx (7/7 - 1)`
`=1/5 xx (1-1)`
`=1/5 xx 0`
`=0`
__________________________________
`3/7 xx 5/8 +3/7 xx 11/8`
`=3/7 xx ( 5/8 + 11/8)`
`=3/7 xx 16/8`
`=3/7 xx 2`
`=6/7`
___________________________________
`6/13 - 12/5 + 7/13 + 17/5`
`=(6/13 + 7/13)+ (17/5 - 12/5)`
`=13/13 + (17/5 - 12/5)`
`=13/13 + 5/5`
`=1+1`
`=2`
___________________________________
`5/8 + 14/18 - 3/8 + 2/9 +14/8`
`=(5/8 - 3/8 + 14/8) + (14/18 + 2/9)`
`=( 5/8 - 3/8 + 14/8) + ( 7/9 + 2/9)`
`=((5-3+14)/8) + ( (7+2)/9)`
`=16/8 + 9/9`
`=2+1`
`=3`
Bài 26:
1.
\(\dfrac{1}{5}\times\dfrac{4}{7}+\dfrac{1}{5}\times\dfrac{3}{7}-\dfrac{1}{5}\\ =\dfrac{1}{5}\times\left(\dfrac{4}{7}+\dfrac{3}{7}\right)-\dfrac{1}{5}\\ =\dfrac{1}{5}-\dfrac{1}{5}=0\)
2.
\(\dfrac{3}{7}\times\dfrac{5}{8}+\dfrac{3}{7}\times\dfrac{11}{8}\\ =\dfrac{3}{7}\times\left(\dfrac{5}{8}+\dfrac{11}{8}\right)\\ =\dfrac{3}{7}\times\dfrac{16}{8}\\ =\dfrac{3}{7}\times2=\dfrac{6}{7}\)
3.
\(\dfrac{6}{13}-\dfrac{12}{5}+\dfrac{7}{13}+\dfrac{17}{5}\\ =\dfrac{6}{13}+\dfrac{7}{13}-\dfrac{12}{5}+\dfrac{17}{5}\\ =1+1=2\)
4.
\(\dfrac{5}{8}+\dfrac{14}{18}-\dfrac{3}{8}+\dfrac{2}{9}+\dfrac{14}{8}\\ =\left(\dfrac{5}{8}-\dfrac{3}{8}+\dfrac{14}{8}\right)+\dfrac{14}{18}+\dfrac{2}{9}\\ =2+\dfrac{14}{18}+\dfrac{2}{9}\\ =\dfrac{36}{18}+\dfrac{14}{18}+\dfrac{4}{18}=\dfrac{54}{18}\\ =3\)
