A) 13/12

B) 401/105

C) 5/13

a)\(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}\)

\(=\frac{5}{6}+\frac{1}{4}\)

\(=\frac{13}{12}\)

b)\(\frac{6}{5}+\frac{4}{3}+\frac{9}{7}\)

\(=\frac{38}{15}+\frac{9}{7}\)

\(=\frac{401}{105}\)

c)\(\frac{90}{108}-\frac{40}{72}\)

\(=\frac{5}{6}+\frac{5}{9}\)

\(=\frac{25}{18}\)

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\(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}\)

\(MSC=12\)

\(\Rightarrow\frac{1}{2}+\frac{1}{3}+\frac{1}{4}=\frac{6}{12}+\frac{4}{12}+\frac{3}{12}\)

\(=\frac{6+4+3}{12}=\frac{13}{12}\)

\(\frac{6}{5}+\frac{4}{3}+\frac{9}{7}\)

\(MSC=105\)

\(\Rightarrow\frac{6}{5}+\frac{4}{3}+\frac{9}{7}=\frac{126}{105}+\frac{140}{105}+\frac{135}{105}\)

\(=\frac{126+140+135}{105}=\frac{401}{105}\)

\(\frac{90}{108}-\frac{40}{72}\)

\(\frac{90}{108}=\frac{5}{6};\frac{40}{72}=\frac{5}{9}\)

\(MSC=54\)

\(\Rightarrow\frac{90}{108}-\frac{40}{72}=\frac{5}{6}-\frac{5}{9}=\frac{45}{54}-\frac{30}{54}\)

\(=\frac{45-30}{54}=\frac{15}{34}\)

\(\frac{8}{9}-\frac{5}{6}=\frac{16}{18}-\frac{15}{18}=\frac{1}{18}\)

\(\frac{90}{108}-\frac{40}{72}=\frac{5}{6}-\frac{5}{9}=\frac{15}{18}-\frac{10}{18}=\frac{5}{18}\)

\(\frac{15}{17}-\frac{11}{13}=\frac{195}{221}-\frac{187}{221}=\frac{8}{221}\)

\(\frac{8}{9}-\frac{5}{6}=\frac{16}{18}-\frac{15}{18}=\frac{1}{18}\)

\(\frac{90}{108}-\frac{40}{72}=\frac{30}{36}-\frac{20}{36}=\frac{10}{36}=\frac{5}{18}\)

tích cho tớ nhé ! ^_^

\(a,\dfrac{90}{108}-\dfrac{40}{72}=\dfrac{5}{6}-\dfrac{5}{9}=\dfrac{30}{36}-\dfrac{20}{36}=\dfrac{10}{36}=\dfrac{5}{18}\)

\(b,\dfrac{59}{8}+\dfrac{21}{4}=\dfrac{59}{8}+\dfrac{42}{8}=\dfrac{101}{8}\)

\(c,\dfrac{25}{2}-\dfrac{18}{13}+\dfrac{5}{13}=\dfrac{325}{26}-\dfrac{26}{26}+\dfrac{10}{26}=\dfrac{309}{26}\)

\(d,\dfrac{17}{13}-\left(\dfrac{25}{100}+\dfrac{4}{13}\right)=\dfrac{17}{13}-\dfrac{29}{52}=\dfrac{3}{4}\)

a) \(\dfrac{90}{108}-\dfrac{40}{72}\)

\(=\dfrac{5}{6}-\dfrac{5}{6}\)

\(=0\)

a) Tìm UCLN (56, 84, 140)

56 = 2³ . 7

84 = 2² . 3 . 7

140 = 2² . 5 . 7

UCLN (56, 84, 140) = 2² . 7 = 28

➤ UCLN (56, 84, 140) = 28

b) BCNN (72, 90, 108)

72 = 2³ . 3²

90 = 2 . 3² . 5

108 = 2² . 3³

BCNN (72, 90, 108) = 2³ . 3³ . 5 = 1080

➤ BCNN (72, 90, 108) = 1080

a, 56 = 2³ . 7 ; 84 = 2² . 3 . 7 ; 140 = 2² . 5 .7

ƯCLN ( 56, 84, 140) : 2² . 7 = 28

b 72 = 2³ . 3²; 90 = 2 . 3² . 5 ; 108 = 2² . 3³

BCNN ( 72, 90, 108 ) : 2³ . 3³ . 5 = 1080

=8

\(\dfrac{72^3.54^2}{108^4}\)

\(=\dfrac{18^3.4^3.18^2.3^2}{18^4.6^4}\)

\(=\dfrac{18^5.2^6.3^2}{18^4.2^4.3^4}\)

\(=\dfrac{18.2^2}{3^2}\)

\(=\dfrac{9.2.2^2}{9}\)

\(=2^3=8\)

\(D=\dfrac{72^3\cdot54^2}{108^4}=\dfrac{2^9\cdot3^6\cdot2^2\cdot3^6}{2^8\cdot3^{12}}=2^3=8\)

kết quả bang 1

\(\frac{72^3.54^2}{108^4}=\frac{108^4.8}{108^4}=8\)

B = \(\frac{6272}{729}\)

a, A= 7+10+13+..+97+100

   Tổng trên có (100-7):3 + 1 = 32 số hạng

Vậy A = (100+7).32/2 = 1712

b, B = 41/90 + 31/72 + 21/40 + -11/45 + -1/36

       = (41/90 + -11/45) + (31/72 + -1/36)

       = (41/90 + -22/90) + (31/72 + -2/72)

       = 19/90 + 29/72

       = 76/360 + 145/360

       = 221/360

a/\(A=7+10+13+...+97+100\)

\(\Rightarrow A=\frac{\left(100+7\right)\left[\left(100-7\right):3+1\right]}{2}\)

\(\Rightarrow A=\frac{107.32}{2}=\frac{3424}{2}=1712\)

a) số lượng số là (100-7):3+1=32 số

tổng của A là (100+7)x32:2=1712