3 + 51 - 21 + 8 = ?
10 + 32 - 4 + 1 = ?
4 + 29 - 5 + 6 = ?
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a ) 420 + 65 . 4 = ( x + 175 ) : 51 + 30
420 + 260 = ( x + 175 ) : 51 + 30
680 = ( x + 175 ) : 51 + 30
=> ( x + 175 ) : 51 = 680 - 30
( x + 175 ) : 51 = 650
x + 175 = 650 . 51
x + 175 = 33150
x = 33150 - 175
x = 32975
b ) ( 32 . 15 ) : 2 = ( x + 70 ) : 14 - 40
480 : 2 = ( x + 70 ) : 14 - 40
240 = ( x + 70 ) : 14 - 40
=> ( x + 70 ) : 14 = 240 + 40
( x + 70 ) : 14 = 280
x + 70 = 280 . 14
x + 70 = 3920
x = 3920 - 70
x = 3850
Tính các tổng sau:
1, S=1-2+3_4+..+25-26
S =-1+3-5+7-...-53+55 ( có 28 số hạng )
= (-1+3)+(-5+7)+...+(-53+55) ( có 28:2=14 nhóm )
= 2+2+...+2
= 2 . 14
= 28
a.\(\dfrac{27}{8}\)
b.\(\dfrac{37}{40}\)
c.\(\dfrac{5}{2}\)
d.\(\dfrac{7}{3}\)
e.5
g.\(\dfrac{53}{16}\)
Bài 1 :
a) \(\dfrac{3}{2}+\dfrac{5}{4}+\dfrac{5}{8}=\dfrac{12}{8}+\dfrac{10}{8}+\dfrac{5}{8}=\dfrac{12+10+5}{8}=\dfrac{27}{8}\)
b) \(\dfrac{4}{5}-\dfrac{3}{8}+\dfrac{2}{4}=\dfrac{32}{40}-\dfrac{15}{40}+\dfrac{20}{40}=\dfrac{32-15+20}{40}=\dfrac{37}{40}\)
c) \(3+\dfrac{6}{8}-\dfrac{5}{4}=\dfrac{3}{1}+\dfrac{6}{8}-\dfrac{5}{4}=\dfrac{24}{8}+\dfrac{6}{8}-\dfrac{10}{8}=\dfrac{20}{8}=\dfrac{5}{2}\)
d) \(\dfrac{5}{6}-\dfrac{1}{2}+2=\dfrac{5}{6}-\dfrac{1}{2}+\dfrac{2}{1}=\dfrac{5}{6}-\dfrac{3}{6}+\dfrac{12}{6}=\dfrac{14}{6}=\dfrac{7}{3}\)
e) \(\dfrac{3}{5}+\dfrac{6}{11}+\dfrac{7}{13}+\dfrac{2}{5}+\dfrac{16}{11}+\dfrac{19}{13}=\left(\dfrac{3}{5}+\dfrac{2}{5}\right)+\left(\dfrac{6}{11}+\dfrac{16}{11}\right)+\left(\dfrac{7}{13}+\dfrac{19}{13}\right)=1+2+2=5\)
g) \(\dfrac{75}{100}+\dfrac{18}{21}+\dfrac{29}{32}+\dfrac{1}{4}+\dfrac{3}{21}+\dfrac{13}{32}=\dfrac{3}{4}+\dfrac{6}{7}+\dfrac{29}{32}+\dfrac{1}{4}+\dfrac{1}{7}+\dfrac{13}{32}=\left(\dfrac{3}{4}+\dfrac{1}{4}\right)+\left(\dfrac{6}{7}+\dfrac{1}{7}\right)+\left(\dfrac{29}{32}+\dfrac{13}{32}\right)=1+1+\dfrac{21}{16}=2+\dfrac{21}{16}=\dfrac{53}{16}\)
1*2*3*4*5*6*7*8*9*10*11*12*13*14*15*16*17*18*19*0*20*21*22*23*24*25*26*27*28*29*30*31*32=0
1+1+2+2+3+3+4+4+...+5+5+6+6
do 4 và 5 cách nhau 1 đơn vị nên dấu " ... " chỉ là đánh lừa
= 12+2232+42+52+62
= 1+4+9+16+25+36
= (1+9) + (4+16) + 25+35+1
= 10 + 20 + 60 + 1
= 30 + 60 + 1
= 90 + 1
= 91
\(3+51-21+8\)
\(=3+51-21+8\)
\(=54-21+8\)
\(=33+8\)
\(=41\)
\(10+32-4+1\)
\(=42-4+1\)
\(=38+1\)
\(=39\)
\(4+29-5+6\)
\(=33-5+6\)
\(=28+6\)
\(=34\)
`3+51-21+8`
`= 54-21+8`
`=33+8`
`=41`
`10+32-4+1`
`=42-4+1`
`=38+1`
`=39`
`4+29-5+6`
`=33-5+6`
`=28+6`
`=34`