Tính bằng cách hợp lí
a. 12 × 3 + 4 × 12 + 36
b. 175 - 25 × 2 - 3 × 25 - 50
1. tính bằng cách hợp lí :
a. 5 . 125 . 2 . 41 . 8 = c. 8 . 12 . 125 . 2 =
b. 25 . 7 . 10 . 4 = d. 4 . 36. 25 . 50 =
a) 5 . 125 . 2 . 41 . 8
= (5 . 8) . (125 . 2) . 41
= 40 . 250 . 41
= 10 000 . 41
= 410 000
b) 25 . 7 . 10 . 4
= (25 . 4 ) . (10 . 7)
= 100 . 70
= 7000
Chúc bạn học tốt!! ^^
a,5.125.2.41.8=(125.8).(2.5).41=1000.10.41=410000
b,25.7.10.4=(25.4).70=100.70=7000
c,8.12.125.2=(8.125).12.2=100.24=2400
d,4.36.25.50=(4.25).(2.50).18=100.100.18=180000
c) 8 . 12 . 125
= (125 . 8) . 12
= 1000 . 12
= 12 000
d) 4 . 36 . 25 . 50
= (25 . 4) . (50 . 36)
= 100 . 1800
= 180 000
Chúc bạn học tốt!! ^^
bài 2: thực hiện phép tính bằng cách hợp lý(nếu có thể)
a)(-31)+(50-19)-(150-31)
b)25.(45-17)-45.(25-17)
c)-1/12 + 4/3
d)3/5 + -5/20+ 30/75 + -7/4
\(a)\)
\(\left(-31\right)+\left(50-19\right)-\left(150-31\right)\)
\(=\left(-31\right)+50-19-150+31\)
\(=\left(-150\right)-19\)
\(=-169\)
\(b)\)
\(25.\left(45-17\right)-45.\left(25-17\right)\)
\(=25.45-25.17-45.25+45.17\)
\(=0\)
\(c)\)
\(\frac{-1}{12}+\frac{4}{3}=\frac{5}{4}\)
\(d)\)
\(3+\frac{-5}{20}+\frac{30}{75}+\frac{-7}{4}\)
\(=\left(\frac{3}{5}+\frac{30}{75}\right)-\left(\frac{5}{20}+\frac{7}{4}\right)\)
\(=1-2\)
\(=-1\)
a) (-31)+(50-19)-(150-31)
= (-31)+50+(-19)-150+(-31)
= (-31)+50-150+(-19)-(-31)
= (-31)+(-100)+12
= -119
b) 25(45-17)-45(25-17)
= 25.45-25.17-45.25-45.17
= 25(45-45)-25(17-17)
= 0
c) -1/12 + 4/3
= -1/12 + 16/12
= 15/12
= 5/4
d) 3/5+(-5)/20+30/75+(-7)/4
= 45/75+30/75+(-5)/20+(-35)/20
= 1+(-2)
= -1
bài 1: tính hợp lí
a) 5 x 72 x 10 x 2 b) 40 x 125 c) 4 x 2021 x 25 d) 16 x 6 x 25
bài 2: tính nhanh
a) 24 x 57 + 43 x 24 b) 12 x 19 + 80 x 12 +12
c) (36 x 15 x 169) : (5 x 18 x13) d) (44 x 52 x 60) : ( 11 x 13 x 15)
bài 3: tìm X
a) X - 280 : 35 = 5 x 54 b) ( X - 280) : 35 = 54 : 4
c) ( X - 128 + 20 ) : 192 = 0 d) 4 x ( X + 200) = 460 + 85 x 4
bài 4: thực hiện phép tính
a) 7/12 - 5/12 b) 8/11 + 19/11 c) 3/8 + 5/12 d) 3/4 + 7/12
bài 5: tìm x
a) X - 6/7 = 5/2 b) 12/7 : X + 2/3 = 7/5
`@` `\text {Ans}`
`\downarrow`
`1,`
`a)`
`5 \times 72 \times 10 \times 2`
`= 5 \times 2 \times 10 \times 72`
`= 10 \times 10 \times 72`
`= 100 \times 72`
`= 7200`
`b)`
`40 \times 125`
`= 4 \times 10 \times 25 \times 5`
`= (5 \times 10) \times (4 \times 25)`
`= 50 \times 100`
`= 5000`
`c)`
`4 \times 2021 \times 25`
`= (4 \times 25) \times 2021`
`= 100 \times 2021`
`= 202100`
`d)`
`16 \times 6 \times 25`
`= 4 \times 4 \times 6 \times 25`
`= (4 \times 25) \times 4 \times 6`
`= 100 \times 24`
`= 2400`
`2,`
`a)`
`24 \times 57 + 43 \times 24`
`= 24 \times (57+43)`
`= 24 \times 100`
`= 2400`
`b)`
`12 \times 19 + 80 \times 12 +12`
`= 12 \times (19 + 80 + 1)`
`= 12 \times 100`
`= 1200`
`c)`
`(36 \times 15 \times 169) \div (5 \times 18 \times 13)`
`= 36 \times 15 \times 169 \div 5 \div 18 \div 13`
`= 6 \times 6 \times 3 \times 5 \times 13 \times 13 \div 5 \div 3 \times 6 \div 13`
`= (6 \div 6) \times (3 \div 3) \times (5 \div 5) \times (13 \div 13) \times 6 \times 13`
`= 6 \times 13`
`= 78`
`d)`
`(44 \times 52 \times 60) \div ( 11 \times 13 \times 15)`
`= 44 \times 52 \times 60 \div 11 \div 13 \div 15`
`= 4 \times 11 \times 13 \times 4 \times 15 \times 4 \div 11 \div 13 \div 15`
`= (11 \div 11) \times (13 \div 13) \times (15 \div 15) \times 4 \times 4 \times`
`= 4 \times 4 \times 4`
`= 64`
`3,`
`a)`
`x - 280 \div 35 = 5 \times 54`
`x - 8 = 270`
`x = 270 + 8`
`x = 278`
`b)`
`(x - 280) \div 35 = 54 \div 4`
`(x - 280) \div 35 = 13,5`
`x - 280 = 13,5 \times 35`
`x - 280 = 472,5`
`x = 472,5 + 280`
`x = 752,5`
`c)`
`(x - 128 + 20) \div 192 = 0`
`x - 128 + 20 = 0 \times 192`
`x - 128 + 20 = 0`
`x - 108 = 0`
`x = 0 + 108`
`x = 108`
`d)`
`4 \times (x + 200) = 460 + 85 \times 4`
`4 \times (x+200) = 460 + 340`
`4 \times (x+200) = 800`
`x + 200 = 800 \div 4`
`x + 200 = 200`
`x = 200 - 200`
`x = 0`
`4,`
`a)`
`7/12 - 5/12`
`= (7 - 5)/12`
`= 2/12`
`= 1/6`
`b)`
`8/11 + 19/11`
`= (8+19)/11`
`= 27/11`
`c)`
`3/8 + 5/12`
`= 9/24 + 10/24`
`= 19/24`
`d)`
`3/4 + 7/12`
`= 9/12 + 7/12`
`= 16/12`
`= 4/3`
`5,`
`a)`
`x - 6/7 = 5/2`
`x = 5/2 + 6/7`
`x = 47/14`
`b)`
`12/7 \div x + 2/3 = 7/5`
`12/7 \div x = 7/5 - 2/3`
`12/7 \div x = 11/15`
`x = 12/7 \div 11/15`
`x = 180/77`
`@` `\text {Kaizuu lv uuu}`
Tính bằng cách hợp lý
a, 5 - ( 1997 - 2005 ) +1997
b, 4567 +(1234 -4567 ) - 4
c, 173 - ( 36 + 173 ) + [( 175 - 27) -175 - (-36 +50 )]
d, 3 x ( 25 : 5 -14 : 2 ) -5 x ( 6 : 2 )
dễ mà : a, 5 - ( 1997 - 2005 ) +1997
= ( 2005 + 5 ) - ( 1997 - 1997 )
= 2010 - 0
= 2010
a, 5 - (1997 -2005 ) + 1997
= 5 - 1997 + 2005 +1997
= (5 + 2005 ) - ( 1997 - 1997)
= 2010 - 0
= 2010
b, 4567 + (1234 - 4567 )-4
= 4567 + 1234 - 4567 -4
= (4567 - 4567 ) + (1234 - 4)
= 0 + 1230
= 1230
c, 173 - ( 36 + 173 ) + [(175 - 27 ) - 175 - ( -36 + 50 )]
= 173 - 36 - 173 + 175 - 27 - 175 - 36 - 50
= ( 173 - 173 ) + (175 - 175 ) - ( 36 + 36 ) - (27 + 50)
= 72 - 77
= -5
d, 3 . (25 : 5 - 14 : 2 ) - 5 . ( 6 : 2)
= 3 (-2) - 5 .3
= 3 ( -2 - 5 )
= 3 . (-7 )
= - 21
a) 5-(1997-2005)+1997
= 5-(-1997)+2005+1997
= (5+2005)+(-1997+1997)
= 2010+0
= 0
b) 4567+(1234-4567)-4
làm tương tự câu a
3. Tính bằng cách thuận tiện nhất:
12/25+3/5+13/25=
3/2+2/3+4/3=
3/2+7/5+3/4=
\(1,\dfrac{12}{25}+\dfrac{3}{5}+\dfrac{13}{25}=\left(\dfrac{12}{25}+\dfrac{13}{25}\right)+\dfrac{3}{5}=1+\dfrac{3}{5}=\dfrac{8}{5}\\ 2,\dfrac{3}{2}+\dfrac{2}{3}+\dfrac{4}{3}=\dfrac{3}{2}+\left(\dfrac{2}{3}+\dfrac{4}{3}\right)=\dfrac{3}{2}+2=\dfrac{7}{2}\\ 3,\dfrac{3}{2}+\dfrac{7}{5}+\dfrac{3}{4}=\left(\dfrac{3}{2}+\dfrac{3}{4}\right)+\dfrac{7}{5}=\left(\dfrac{6}{4}+\dfrac{3}{4}\right)+\dfrac{7}{5}=\dfrac{9}{4}+\dfrac{7}{5}=\dfrac{45}{20}+\dfrac{28}{20}=\dfrac{73}{20}\)
Quy đồng 3/5 cho cùng mẫu chung là 25 có
12/25+15/25+13/25=40/25=8/5
Mẫu chung là 6 có
9/6+4/6+8/6=21/6=7/2
Quy đồng mẫu chung là 20 có
30/20+28/30+15/20=73/20
Chúc em học tốt
12/25 + 3/5 + 13/25 = (12/25 +13/25) + 3/5 = 1 + 3/5 = 8/5
3/2 + 2/3 + 4/3 =3/2 + ( 2/3+4/3 ) = 7/2
3/2 + 7/5 + 3/4 = ( 3/2+3/4) + 7/5 = 12/5
Tính bằng cách thuận tiện nhất :
a) 12/25+3/5+13/25
b) 3/2+2/3+4/3
c) 3/5+7/5+3/4
Tính bằng cách hợp lí:
a) (9/25 - 2 . 18 ) / (19/5 + 0,2 )
b) 12 . (-2/3)^2 + 4/3
a) \(=\frac{\left(\frac{9}{25}-36\right)}{\frac{19}{5}+\frac{1}{5}}=\frac{\frac{9}{25}-\frac{900}{25}}{\frac{20}{5}}=\frac{-891}{25}:4\)\(=\frac{-891}{25\cdot4}=\frac{-891}{100}=-8,91\)
b) \(=12\cdot\frac{\left(-2\right)^2}{3^2}+\frac{4}{3}=12\cdot\frac{4}{9}+\frac{4}{3}\)\(=\frac{48}{9}+\frac{4}{3}=\frac{48}{9}+\frac{12}{9}=\frac{60}{9}\)
tính giá trị biểu thức sau bằng cách hợp lí
a)A=27x36+73.99+27x14-49x73
b)B=(\(4^5\) x 10 x 5\(^6\) + 25\(^5\) x 2\(^8\) ): (2\(^8\) x 5\(^4\) + 5\(^7\) x 2\(^5\) )
a) \(A=27\cdot36+73\cdot99+27\cdot14-49\cdot73\)
\(A=27\cdot\left(36+14\right)+73\cdot\left(99-49\right)\)
\(A=27\cdot50+73\cdot50\)
\(A=50\cdot\left(27+73\right)\)
\(A=50\cdot100\)
\(A=5000\)
b) \(B=\left(4^5\cdot10\cdot5^6+25^5\cdot2^8\right):\left(2^8\cdot5^4+5^7\cdot2^5\right)\)
\(B=\dfrac{\left(2^2\right)^5\cdot2\cdot5\cdot5^6+\left(5^2\right)^5\cdot2^8}{2^8\cdot5^4+5^7\cdot2^5}\)
\(B=\dfrac{2^{11}\cdot5^7+5^{10}\cdot2^8}{2^8\cdot5^4+5^7\cdot2^5}\)
\(B-\dfrac{2^8\cdot5^7\cdot\left(2^3\cdot1+5^3\cdot1\right)}{2^5\cdot5^4\cdot\left(2^3\cdot1+5^3\cdot1\right)}\)
\(B=\dfrac{2^8\cdot5^7}{2^5\cdot5^4}\)
\(B=2^3\cdot5^3\)
\(B=10^3\)
\(B=1000\)
Tính tổng sau bằng cách hợp lí
A = \(\dfrac{1}{4}+\dfrac{1}{12}+\dfrac{1}{36}+...+\dfrac{1}{972}+\dfrac{1}{2916}\)
A=14+112+136+...+1972+12916
3A=34+14+112+...+1324+1972
3A−A=(34+14+112+...+1324+1972)−(14+112+136+...+1972+12916)
2A=34−12916
A=10932916