1) Tính
a) 38 / 45 - (8 / 45 - 17 / 51 - 3 / 11 )
b) 1 / 3 + 12 / 67 + 13 / 41 - ( 79 / 67 - 28 / 41)
2) Tìm số nguyên a,b biết:
a) a / 3 - 4 / b = 1 / 5
b) a / 5 - 2 / b = 1 / 30
c) 5 / a - b / 3 = 1 / 6
d) 4 /7 < a / b < 2 / 3 và 7a +4b = 1994
Tính nhanh
a) 31/23 - (7/32 + 8/23)
b) 38/45 - (8/45 - 17/51 - 3/11)
c)(1/3 + 12/67 + 13/41) - ( 79/67 - 28/41)
d) 1/5 + -1/6 + 1/7 + -1/8 + 1/9 + 1/8 + -1/7 + 1/6 + -1/5
Tính nhanh
a) 31/23 - (7/32 + 8/23)
b) 38/45 - (8/45 - 17/51 - 3/11)
c)(1/3 + 12/67 + 13/41) - ( 79/67 - 28/41)
d) 1/5 + -1/6 + 1/7 + -1/8 + 1/9 + 1/8 + -1/7 + 1/6 + -1/5
`a,`
`31/23-(7/32+8/23)`
`=31/23-7/32-8/23`
`=(31/23-8/23)-7/32`
`=1-7/32=25/32`
`b,`
`38/45-(8/45-17/51-3/11)`
`=38/45-8/45+17/51+3/11`
`= (38/45-8/45)+17/51+3/11`
`=2/3+17/51+3/11`
`=1+3/11=14/11`
`c,`
`(1/3+12/67+13/41)-(79/67-28/41)`
`= 1/3+12/67+13/41-79/67+28/41`
`= 1/3+(12/67-79/67)+(13/41+28/41)`
`= 1/3+(-1)+1=1/3+(-1+1)=1/3+0=1/3`
`d,`
`1/5+(-1/6)+1/7+(-1/8)+1/9+1/8+(-1/7)+1/6+(-1/5)`
`= (1/5+ -1/5)+(-1/6+1/6)+(1/7+ -1/7)+(-1/8 +1/8)+1/9`
`= 0+0+0+0+1/9=1/9 .`
tính bằng cách hợp lí nhất
a) 31/23 - (7/23 + 8/23)
b) (1/3 + 12/67 + 13/41 ) - (79/67 - 28/41 )
c) 38/45 - ( 8/45 - 17/51- 3/11 )
Tính hợp lí: a. 31/23 - (7/23 + 8/23). b.(1/3 + 12/67+13/41) - (79/67 - 28/41). c. 38/45 - (8/45 - 17/51 - 3/11)
\(a\frac{31}{23}-\left(\frac{7}{23}+\frac{8}{23}\right)\)
\(=\frac{31}{23}-\frac{7}{23}-\frac{8}{23}\)
\(=\frac{16}{23}\)
Hot
tốt
!
a)\(\frac{31}{23}-\left(\frac{7}{23}+\frac{8}{23}\right)=\frac{31}{23}-\frac{8}{23}+\frac{7}{23}=1+\frac{7}{23}=1\frac{7}{23}\)
b)\(\left(\frac{1}{3}+\frac{12}{67}+\frac{13}{41}\right)-\left(\frac{79}{67}-\frac{28}{41}\right)=\left(\frac{13}{41}+\frac{28}{41}\right)+\left(\frac{79}{67}-\frac{12}{67}\right)-\frac{1}{3}=1+1-\frac{1}{3}\)
\(=2-\frac{1}{3}=\frac{5}{3}\)
2/15-2/65-4/39
32/13-(7/23+8/23)
(1/3+12/67+13/41) - (79/67 - 28/41)
38/45 - (8/45-17/51-3/11)
2/15-2/65-4/39=4/39-4/39=0
32/13-(7/23+8/23)=32/13-15/23=541/299
(1/3+12/67+13/41) - (79/67 - 28/41)=6836/8241-1363/2747=1/3
38/145 - (8/45-17/51-3/11)=38/145-(-212/495)=1982/2871
9/10 - 13/75 - 1/6
2/15 - 2/65 - 4/39
31/23 - (7/32 + 8/23)
(1/3+12/67+13/41) - (79/67 - 28/41)
38/45 - (8/45 - 17/51- 3/11)
a/\(\left(\frac{1}{3}+\frac{12}{67}+\frac{13}{41}\right)-\left(\frac{79}{67}-\frac{28}{41}\right)\)
b/ \(\frac{38}{45}-\left(\frac{8}{45}-\frac{17}{51}-\frac{3}{11}\right)\)
a)
\(\left(\frac{1}{3}+\frac{12}{67}+\frac{13}{41}\right)-\left(\frac{79}{67}-\frac{28}{41}\right)\)
= \(\frac{1}{3}+\frac{12}{67}+\frac{13}{41}-\frac{79}{67}+\frac{28}{41}\)
= \(\frac{1}{3}+\left(\frac{12}{67}-\frac{79}{67}\right)+\left(\frac{13}{41}+\frac{28}{41}\right)\)
= \(\frac{1}{3}+\left(-1\right)+1\)
= \(\frac{1}{3}+0=\frac{1}{3}\)
b)
\(\frac{38}{45}-\left(\frac{8}{45}-\frac{17}{51}-\frac{3}{11}\right)\)
= \(\frac{38}{45}-\frac{8}{45}+\frac{17}{51}+\frac{3}{11}\)
= \(\left(\frac{38}{45}-\frac{8}{45}\right)+\left(\frac{17}{51}+\frac{3}{11}\right)\)
= \(\frac{2}{3}+\frac{20}{33}\)
= \(\frac{14}{11}\)
1) Tính hợp lý
a)\(\frac{31}{23}-\left(\frac{7}{32}+\frac{8}{32}\right)\)
b)\(\left(\frac{1}{3}+\frac{12}{67}+\frac{13}{41}\right)-\left(\frac{79}{67}-\frac{28}{41}\right)\)
c)\(\frac{38}{45}-\left(\frac{8}{45}-\frac{17}{51}-\frac{3}{11}\right)\)
d)\(\left(\frac{17}{28}+\frac{18}{29}-\frac{19}{30}-\frac{30}{31}\right).\left(-\frac{5}{12}+\frac{1}{4}+\frac{1}{6}\right)\)
Trả lời
b)(1/3+12/67+13/41)-(79/67-28/41)
=1/3+12/67+13/41-79/67+28/41
=1/3+(12/67-79/67)+(13/41+28/41)
=1/3+(-67/67)+41/41
=1/3+(-1)+1
=1/3+0
=1/3.
c)38/45-(8/45-17/51-3/11)
=38/45-8/45+17/51+3/11
=30/45+1/3+3/11
=2/3+1/3+3/11
=3/3+3/11
=1+3/11
=1 3/11.
d)(17/28+18/29-19/30-30/31).(-5/12+1/4+1/6)
=(17/28+18/29+19/30+30/31).(-5+3+2/12)
=(17/28+18/29+19/30+30/31).0
=0.
bài 20 tính bằng phương pháp hợp lí nhất
a \(\frac{31}{23}-\left(\frac{7}{32}+\frac{8}{23}\right)\)
b \(\left(\frac{1}{3}+\frac{12}{67}+\frac{13}{41}\right)-\left(\frac{79}{67}-\frac{28}{41}\right)\)
c\(\frac{38}{45}-\left(\frac{8}{45}-\frac{17}{51}-\frac{3}{11}\right)\)