tính một cách hợp lí
(9-8-7-6-5-4-3-2-1).(500.9-250.18)
Tính hợp lý:
a) 815 - 23 - 77 + 185
b) 3145 - 246 + 2347 - 145 + 4246 - 347
c) 2018 : 1 - 2018 . 1 : 2018 . 2008 + 2018 . 2002
d) 9 - 8 - 7 - . . . - 2 - 1 . ( 500 . 9 - 250 . 18 )
Tính hợp lý:
a, 815 – 23 – 77 + 185
b, 3145 – 246 +2347 – 145 + 4246 – 347
c, (2018:1 – 2018.1):(2018.2008 + 2018.2002)
d, (9 – 8 – 7 – … – 2 – 1).(500.9 – 250.18)
a) 815 – 23 – 77 +185 = (815 + 185) – (23+77) = 1000 – 100 = 900
b) 3145 – 246 + 2347 – 145 + 4246 – 347
= (3145-145) + (4246 – 246) + (2347 – 347)
= 3000 + 4000 + 2000 = 9000
c) (2018:1 – 2018.1):(2018.2008+2018.2002) = 0 : (2018.2008+2018.2002) = 0
d) (9 – 8 – 7 – 6 – … – 2 – 1).(500.9 – 250.18)
= (9 – 8 – 7 – 6 – … – 2 – 1).(500.9 – 250.2.9)
= (9 – 8 – 7 – 6 – … – 2 – 1).(500.9 – 500.9)
= (9 – 8 – 7 – 6 – … – 2 – 1).0 = 0
Bài 2. Tính nhanh:
a) 27.19 + 73.20
b) 42.50 - 38.50 - 25.4
e) 254.58 + 21.508
c) 12.53 + 53.172 - 53.84
d) 2.31.12 + 4.6.42 + 8.27.3
f) (9 - 8 - 7 -... - 2 -1).(500.9 - 250.18)
Mn giúp e vs ạ, em chuẩn bị phải nộp bài rùi T - T
\(a,=27\cdot20+73\cdot20-27=20\left(27+73\right)-27\\ =20\cdot100-27=2000-27=1973\\ b,=42\cdot50-38\cdot50-50\cdot2=50\left(42-38-2\right)=50\cdot2=100\\ e,=254\left(58+21\cdot2\right)=254\cdot100=25400\\ c,=53\left(12+172-84\right)=53\cdot100=5300\\ d,=24\left(31+42+27\right)=24\cdot100=2400\\ f,=\left(9-8-...-1\right)\left(500\cdot9-500\cdot9\right)=\left(9-8-...-1\right)\cdot0=0\)
a. 27*(20-1)+73*20=27*20-27+73*20=20*(27+73)-27=20*100-27=2000-27=1973
b. =42*50-38*50-50*2=50*(42-38-2)=50*2=100
C. =53*(12+172-84)=53*100=5300
D.=31*24+24*42+24*27=24*(31+42+27)=24*100=2400
E.=508*29+21*508=508*(29+21)=508*50=25400
Tính nhanh một cách hợp lí :
1/2 + 2/3 - 3/4 × 4/5 × 5/6 × 6/7 × 7/8 × 8/9 × ......................... × 29/30 : 6/10
1/2 + 2/3 - 3/4 * 4/5 * 5/6 * 6/7 * 7/8 * 8/9 *...* 29/30 : 6/10
= 1/2 + 2/3 - 1/10 : 6/10
= 1/2 + 2/3 - 1/6
= 1
27 . 19 + 73 . 20
25254.58 + 21.508
(9 - 8 - 7 -... - 2 -1) . (500.9 - 250.18)
có ai biết trình bày chi tiết của bài này k ạ?
mn giúp em với tối nay em phải nộp T - T
27 . 19 + 73 . 20
= 27 . 19 + 73 . 19 + 73
= 19 . (27 + 73) + 73
= 19 . 100 + 73
= 1900 + 73
= 1973
25254 . 58 + 21 . 508
= 25254 . 50 + 25254 . 8 + 21 . 500 + 21 . 8
= 25254 . 50 + 25254 . 8 + 210 . 50 + 21 . 8
= (25254 . 50 + 210 . 50) + (25254 . 8 + 21 . 8)
= [50 . (25254 + 210)] + [8. (25254 + 21)]
= (50 . 25464) + (8 . 25275)
= 1273200 + 202200
= 1475400
Tính một cách hợp lí:
1-2+3-4+5-6+7-8+9-10+......+51-52+53
hello bạn lớp mấy vậy???
=(1-2)+(3-4)+...+(51-52)+53
= -1 + -1 + ... + -1 + 53
= -1 x (52:2)+53
= -26 + 53
=27
= (1-2)+(3-4)+...+(51-52)+53
= (-1) + (-1) + (-1) + ... + (-1) + 53
= -1 x (52 : 2) + 53
= -26 + 53
=27 nhớ tích and kết bạn
bài 5: tính giá trị biểu thức sau một cách hợp lí
A = -7/21 + ( 1+1/3) B=2/15 +(5/9+ -6/9)
C=9-1/5 + 3/12 ) + -3/4
bài 6
a) x + 7/8 = 13/12 b) - (-6)/12 - x = 9/48
c) x+ 4/6 = 5/25 - (-7)/15 c) x + 4/5 = 6/20 - (-7)/3
`5`
`a, -7/21 +(1+1/3)`
`=-7/21 + ( 3/3 + 1/3)`
`=-7/21+ 4/3`
`=-7/21+ 28/21`
`= 21/21`
`=1`
`b, 2/15 + ( 5/9 + (-6)/9)`
`= 2/15 + (-1/9)`
`= 1/45`
`c, (9-1/5+3/12) +(-3/4)`
`= ( 45/5-1/5 + 3/12)+(-3/4)`
`= ( 44/5 + 3/12)+(-3/4)`
`= 9,05 +(-0,75)`
`=8,3`
`6`
`x+7/8 =13/12`
`=>x= 13/12 -7/8`
`=>x=5/24`
`-------`
`-(-6)/12 -x=9/48`
`=> 6/12 -x=9/48`
`=>x= 6/12-9/48`
`=>x=5/16`
`---------`
`x+4/6 =5/25 -(-7)/15`
`=>x+4/6 =1/5 + 7/15`
`=> x+ 4/6=10/15`
`=>x=10/15 -4/6`
`=>x=0`
`----------`
`x+4/5 = 6/20 -(-7)/3`
`=>x+4/5 = 6/20 +7/3`
`=>x+4/5 = 79/30`
`=>x=79/30 -4/5`
`=>x= 79/30-24/30`
`=>x= 55/30`
`=>x= 11/6`
\(5)\)
\(A=\dfrac{-7}{21}+\left(1+\dfrac{1}{3}\right)\)
\(A=\dfrac{-7}{21}+\dfrac{4}{3}\)
\(A=\dfrac{-7}{21}+\dfrac{28}{21}\)
\(A=1\)
\(--------------\)
\(B=\dfrac{2}{15}+\left(\dfrac{5}{9}+\dfrac{-6}{9}\right)\)
\(B=\dfrac{2}{15}+\dfrac{-1}{9}\)
\(B=\dfrac{18}{135}+\dfrac{-15}{135}\)
\(B=\dfrac{1}{45}\)
\(------------\)
\(C=9-\dfrac{1}{5}+\dfrac{3}{12}+\dfrac{-3}{4}\)
\(C=\dfrac{44}{5}+\dfrac{3}{12}+\dfrac{-3}{4}\)
\(C=\dfrac{528}{60}+\dfrac{15}{60}+\dfrac{-3}{4}\)
\(C=\dfrac{181}{20}+\dfrac{-3}{4}\)
\(C=\dfrac{181}{20}+\dfrac{-15}{20}\)
\(C=\dfrac{83}{10}\)
\(6)\)
\(a)\) \(x+\dfrac{7}{8}=\dfrac{13}{12}\)
\(x=\dfrac{13}{12}-\dfrac{7}{8}\)
\(x=\dfrac{104}{96}-\dfrac{84}{96}\)
\(x=\dfrac{5}{24}\)
\(b)\) \(\dfrac{-6}{12}-x=\dfrac{9}{48}\)
\(\dfrac{-1}{2}-x=\dfrac{3}{16}\)
\(x=\dfrac{-1}{2}-\dfrac{3}{16}\)
\(x=\dfrac{-8}{16}-\dfrac{3}{16}\)
\(x=\dfrac{-11}{16}\)
\(c)\) \(x+\dfrac{4}{6}=\dfrac{5}{25}-\left(-\dfrac{7}{15}\right)\)
\(x+\dfrac{4}{6}=\dfrac{5}{25}+\dfrac{7}{15}\)
\(x+\dfrac{4}{6}=\dfrac{75}{375}+\dfrac{105}{375}\)
\(x+\dfrac{4}{6}=\dfrac{12}{25}\)
\(x=\dfrac{12}{25}-\dfrac{4}{6}\)
\(x=\dfrac{72}{150}-\dfrac{100}{150}\)
\(x=\dfrac{-14}{75}\)
\(d)\) \(x+\dfrac{4}{5}=\dfrac{6}{20}-\left(-\dfrac{7}{3}\right)\)
\(x+\dfrac{4}{5}=\dfrac{6}{20}+\dfrac{7}{3}\)
\(x+\dfrac{4}{5}=\dfrac{18}{60}+\dfrac{140}{60}\)
\(x+\dfrac{4}{5}=\dfrac{79}{30}\)
\(x=\dfrac{79}{30}-\dfrac{4}{5}\)
\(x=\dfrac{79}{30}-\dfrac{24}{30}\)
\(x=\dfrac{11}{6}\)
Giải:
\(A=\dfrac{-7}{21}+\left(1+\dfrac{1}{3}\right)\)
\(A=\dfrac{-7}{21}+\dfrac{4}{3}\)
\(A=\dfrac{-7}{21}+\dfrac{28}{21}\)
\(A=\dfrac{21}{21}=1\)
\(B=\dfrac{2}{15}+\left(\dfrac{5}{9}+\dfrac{-6}{9}\right)\)
\(B=\dfrac{2}{15}+\dfrac{-1}{9}\)
\(B=\dfrac{6}{45}+\dfrac{-5}{45}\)
\(B=\dfrac{1}{45}\)
\(C=\left(9-\dfrac{1}{5}+\dfrac{3}{12}\right)+\dfrac{-3}{4}\)
\(C=\left(\dfrac{44}{5}+\dfrac{1}{4}\right)+\dfrac{-3}{4}\)
\(C=\dfrac{181}{20}+\dfrac{-3}{4}\)
\(C=\dfrac{181}{20}+\dfrac{-15}{20}\)
\(C=\dfrac{166}{20}\)
Bài 6:
\(a)x+\dfrac{7}{8}=\dfrac{13}{12}\)
⇔\(x=\dfrac{13}{12}-\dfrac{7}{8}=\dfrac{5}{24}\)
\(b)\dfrac{-6}{12}-x=\dfrac{9}{48}\)
⇔\(x=\dfrac{-6}{12}-\dfrac{9}{48}=\dfrac{-11}{16}\)
\(c)x+\dfrac{4}{6}=\dfrac{5}{25}-\dfrac{-7}{15}\)
\(\Leftrightarrow x+\dfrac{2}{3}=\dfrac{2}{3}\)
\(\Leftrightarrow x=\dfrac{2}{3}-\dfrac{2}{3}=0\)
\(d)x+\dfrac{4}{5}=\dfrac{6}{20}-\dfrac{-7}{3}\)
⇔\(x+\dfrac{4}{5}=\dfrac{79}{30}\)
⇔\(x=\dfrac{79}{30}-\dfrac{4}{5}=\dfrac{11}{6}\)
Thực hiện các phép tính sau một cách hợp lí
13 - 12 + 11 + 10 - 9 + 8 - 7 - 6 + 5 - 4 + 3 + 2 - 1
13 - 12 + 11 + 10 - 9 + 8 - 7 - 6 + 5 - 4 + 3 + 2 - 1
= 1 + 11 - 1 + 1 + 11 - 7 + 1
= 12 - 1 + 1 + 11 - 7 + 1
= 11 + 1 + 11 - 7 + 1
= 12 + 11 - 7 + 1
= 23 - 7 + 1
= 16 + 1
=17
BẰNG 13 NHÉ BẠN .TK CHO MÌNH NHA .
CHÚC BẠN HỌC TỐT
Thực hiện các phép tính sau một cách hợp lí :A=1+2-3-4+5+6-7-8+9+10-11-...+298-299+300+301+302-303
Lời giải:
$A=(1+2-3-4)+(5+6-7-8)+(9+10-11-12)+....+(297+298-299-300)+301+302-303$
$=(-4)+(-4)+(-4)+....+(-4)+300$
Số lần xuất hiện của $-4$ là:
$[(300-1):1+1]:4=75$
$A=(-4),75+300=0$