Tính: 3 7 + 5 14
A. 8 21
B. 77 14
C. 11 14
D. 5 7
Bài 1 : tính
A ) 7 / 8 + 5 / 12 = B ) 19 / 15 - 5 / 6 =
C ) 8 / 21 x 14 / 5 = D ) 9 / 7 : 3 / 4 =
Bài 1 : tính
`A ) 7 / 8 + 5 / 12 = 21/24 + 10/24 = 31/24`
`B ) 19 / 15 - 5 / 6 = 38/30 - 25/30 = 13/30 `
`C ) 8 / 21 xx 14 / 5 =16/15 `
`D ) 9 / 7 : 3 / 4 = 9/7 xx 4/3 = 12/7`
\(a,\dfrac{7}{8}+\dfrac{5}{12}=\dfrac{21}{24}+\dfrac{10}{24}=\dfrac{31}{24}\\ b,\dfrac{19}{15}-\dfrac{5}{6}=\dfrac{38}{30}-\dfrac{25}{30}=\dfrac{13}{30}\\ c,\dfrac{8}{21}\times\dfrac{14}{5}=\dfrac{16}{15}\\ d,\dfrac{9}{7}:\dfrac{3}{4}=\dfrac{9}{7}\times\dfrac{4}{3}=\dfrac{12}{7}\)
Tính bằng cách thuận tiện nhất:
a)1678*24+77*1678-1678
b)2/5 + 4/11 + 3/5 + 18/11 + 1/4 +1/6
c) 7/9x7 + 7/9x4 - 7/9x10
e)13/7x 2/3 - 6/7 : 6/4 +14/21
g)5/9x2/6+-5/9x3/6
a) \(1678\cdot24+77\cdot1678-1678=1678\left(24+77-1\right)=167800\)
b) Ta có: \(\dfrac{2}{5}+\dfrac{4}{11}+\dfrac{3}{5}+\dfrac{18}{11}+\dfrac{1}{4}+\dfrac{1}{6}\)
\(=\left(\dfrac{2}{5}+\dfrac{3}{5}\right)+\left(\dfrac{4}{11}+\dfrac{18}{11}\right)+\dfrac{1}{4}+\dfrac{1}{6}\)
\(=3+\dfrac{1}{4}+\dfrac{1}{6}\)
\(=\dfrac{36}{12}+\dfrac{3}{12}+\dfrac{2}{12}=\dfrac{41}{12}\)
c) \(\dfrac{7}{9\cdot7}+\dfrac{7}{9\cdot4}-\dfrac{7}{9\cdot10}\)
\(=\dfrac{7}{9}\left(\dfrac{1}{7}+\dfrac{1}{4}-\dfrac{1}{10}\right)\)
\(=\dfrac{7}{9}\cdot\left(\dfrac{20}{140}+\dfrac{35}{140}-\dfrac{14}{140}\right)\)
\(=\dfrac{7}{9}\cdot\dfrac{41}{140}=\dfrac{41}{180}\)
Tính bằng hai cách (theo mẫu):
Mẫu: (35 -21): 7 = ?
Cách 1: (35 -21): 7
= 14 :7 =2
Cách 2: (35 -21): 7
= 35 : 7 - 21 : 7 = 5 - 3 = 2
a) (27 -18) : 3;
b) (64 - 32) : 8
a) (27 -18) : 3 =?
Cách 1: (27 -18) : 3
= 9 : 3 = 3
Cách 2:(27 -18) : 3
= 27 : 3 - 18 : 3
= 9 - 6 = 3
b) (64 - 32) : 8 = ?
Cách 1:(64 - 32) : 8
= 32 : 8 = 4
Cách 2:(64 - 32) : 8
= 64 : 8 - 32 : 8
= 8 - 4 = 4
Nói thêm: Khi chia một hiệu cho một số, ta có thể chia số bị trừ và số trừ cho số đó (nếu chia hết), rồi trừ hai kết quả cho nhau.
(27 -18) : 3
= 27 : 3 - 18 : 3
a)7/8 : (14/3 +7/2) + 4/28=
b)21-3/4 : (3/4- 1/3 )=
c) (6 - 14/5) ✖️ 25/8 + 18/5 :1/4=
1. Tính
a, 11/15 + - 7/10 + 13/30
b, 7/9 + -1/4 + 3/5
c, -5/21 + -5/14 + 4/35
d, 2/7 + 1/9 + 1/7 + 5/9 + 8/14
e, -4/9 + 8/15 + -2/11 + 5/-9 + 7/15
Tính nhanh:
a) -5/9 - 4/15 + 2/9 -11/15
b -8/13 - 7/16 + 21/13 - 1/6
c -15/25 - 14/21 + 8/5 - 5/3
giúp mình v chiều về m đi học r
a,9/4-[-11}/-4
b, 7/8-3/-8-1/8
c,-5/21-25/21-[-1]/21
d, 18/24-35/-10
e, 3/7-11/14-19/28
g, 5/-{-2}/3-1/12
h, 3/17-{-5}/13-{-18}/35-14/17-17/{-35}-{-8}/13
a; \(\dfrac{9}{4}\) - \(\dfrac{-11}{4}\)
= \(\dfrac{9}{4}\) + \(\dfrac{11}{4}\)
= \(\dfrac{20}{4}\)
= 5
b; \(\dfrac{7}{8}\) - \(\dfrac{3}{-8}\) - \(\dfrac{1}{8}\)
= \(\dfrac{7}{8}\) + \(\dfrac{3}{8}\) - \(\dfrac{1}{8}\)
= \(\dfrac{7+3-1}{8}\)
= \(\dfrac{9}{8}\)
c; \(\dfrac{-5}{21}\) - \(\dfrac{25}{21}\) - \(\dfrac{-1}{21}\)
= \(\dfrac{-5}{21}\) - \(\dfrac{25}{21}\) + \(\dfrac{1}{21}\)
= \(\dfrac{-5-25+1}{21}\)
= \(\dfrac{-29}{21}\)
Tính A = 1/5*6 +3/6*9 + 5/9*14 + 7/14* 21 + 9/21*30
A = \(\frac{1}{5\times6}+\frac{3}{6\times9}+\frac{5}{9\times14}+\frac{7}{14\times21}+\frac{9}{21\times30}\)
A = \(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{9}+\frac{1}{9}-\frac{1}{14}+\frac{1}{14}-\frac{1}{21}+\frac{1}{21}-\frac{1}{30}\)
A = \(1-\frac{1}{30}\)
A = \(\frac{29}{30}\)
Tính
a.3/5 + 5/8
b.21/40 - 3/8
c.5/7 *12/11
d.15/7 : 5/14
a,3/5+5/8=24/40+25/40=49/40
b,21/40-3/8=21/40-15/40=6/40=3/20
c5/7*12/11=5*12/7*11=60/77
d.15/7:5/14=15/7*14/5=6
hãy tính nhanh:
A.1+2+3+4+5+6+7+8+9+10+11+12+13-14=?
B.30-29+28-27+26-25+24-23+22-21...+12-11+10-9+8-7+6-5+4-3+2-1=?