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\(a)\frac{5}{12}+\frac{3}{14}+\frac{7}{12}=\left(\frac{5}{12}+\frac{7}{12}\right)+\frac{3}{4}=1+\frac{3}{4}=\frac{7}{4}\)
\(b)\frac{15}{14}\times\frac{17}{18}\times\frac{28}{15}=\frac{15\times17\times28}{14\times18\times15}=\frac{17}{9}\)
\(c)\frac{5}{8}\times\frac{5}{4}+\frac{5}{4}\times\frac{3}{8}=\frac{5}{4}\times\left(\frac{5}{8}+\frac{3}{8}\right)=\frac{5}{4}\times1=\frac{5}{8}\)
Bài 2:
Sau 2 giờ con ốc sên bò được:
1/5+1/6=11/30(cây cột)
Sau 2 giờ thì con ốc sên còn phải bò:
1-11/30=19/30(cây cột)
a: \(=\dfrac{17}{19}\cdot\dfrac{19}{17}\cdot\dfrac{4}{5}=\dfrac{4}{5}\)
b: \(=\dfrac{14}{7}\cdot\dfrac{7}{6}=2\cdot\dfrac{7}{6}=\dfrac{14}{6}=\dfrac{7}{3}\)
c: =13/14(4/5+1/5)=13/14
\(\dfrac{17}{19}\times\dfrac{12}{15}\times\dfrac{19}{17}.\\ =\dfrac{17}{19}\times\dfrac{19}{17}\times\dfrac{12}{15}.\\ =1\times\dfrac{12}{15}=\dfrac{12}{15}.\\ \left(\dfrac{5}{7}+\dfrac{9}{7}\right)\times\dfrac{21}{18}.\\ =2\times\dfrac{7}{6}=\dfrac{7}{3}.\\ \dfrac{4}{5}\times\dfrac{13}{14}+\dfrac{13}{14}\times\dfrac{1}{5}.\\ =\left(\dfrac{4}{5}+\dfrac{1}{5}\right)\times\dfrac{13}{14}.\\ =1\times\dfrac{13}{14}.\\ =\dfrac{13}{14}.\)
\(\dfrac{11}{12}x\dfrac{6}{9}-\dfrac{3}{8}=\dfrac{66}{108}-\dfrac{3}{8}=\dfrac{17}{72}\)
\(\dfrac{5}{7}:\dfrac{9}{14}-\dfrac{17}{18}=\dfrac{70}{63}-\dfrac{17}{18}=\dfrac{1}{6}\)
\(\dfrac{11}{12}\) x \(\dfrac{6}{9}-\dfrac{3}{8}=\dfrac{11}{18}-\dfrac{3}{8}=\dfrac{88}{144}-\dfrac{54}{144}=\dfrac{34}{144}=\dfrac{17}{72}\)
\(\dfrac{5}{7}:\dfrac{9}{14}-\dfrac{17}{18}\)\(=\dfrac{5}{7}\) x \(\dfrac{14}{9}-\dfrac{17}{18}=\dfrac{10}{9}-\dfrac{17}{18}=\dfrac{20}{18}-\dfrac{17}{18}=\dfrac{3}{18}=\dfrac{1}{6}\)
Tính nhanh mỗi biểu thức sau:
a, 0 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20
= (0 + 20) + (1 + 19) + (2 + 18) + (3 + 17) + (4 + 16) + (5 + 15) + (6 + 14) + (7 + 13) + (8 + 12) + (9 + 11) + 10
= 20 + 20 + 20 + 20 + 20 + 20 + 20 + 20 + 20 + 20 + 10
= 20 x 10 + 10
= 200 + 10
= 210
b, 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x (4 x 9 - 36)
= 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x (36 - 36)
= 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x 0
= A x 0
= 0
c, (81 - 7 x 9 - 18) : (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9)
= (81 - 63 - 18) : (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9)
= (18 - 18) : (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9)
= 0 :(1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9)
= 0 : A
= 0
d, (6 x 5 + 7 - 37) x (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10)
= (30 + 7 - 37) x (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10)
= (37 - 37) x (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10)
= 0 x (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10)
= 0 x A
= 0
e, (11 x 9 - 100 + 1) : (1 x 2 x 3 x 4 x ... x 10)
= (99 - 100 + 1) : (1 x 2 x 3 x 4 x ... x 10)
= (99 + 1 - 100) : (1 x 2 x 3 x 4 x ... x 10)
= (100 - 100) : (1 x 2 x 3 x 4 x ... x 10)
= 0 : (1 x 2 x 3 x 4 x ... x 10)
= 0 : A
= 0
g, (m : 1 - m x 1) : (m x 2008 + m x 2008)
= (m - m) : (m x 2008 + m x 2008)
= 0 : (m x 2008 + m x 2008)
= 0 : A
= 0
h, (2 + 4 + 6 + 8 + m x n) x (324 x 3 - 972)
= (2 + 4 + 6 + 8 + m x n) x (972 - 972)
= (2 + 4 + 6 + 8 + m x n) x 0
= A x 0
= 0
l, (1 + 2 + 3 + ... + 99) x (13 x 15 - 12 x 15 - 15)
= (1 + 2 + 3 + ... + 99) x (15 x (13 - 12 - 1))
= (1 + 2 + 3 + ... + 99) x (15 x 0)
= (1 + 2 + 3 + ... + 99) x 0
= A x 0
= 0
i, (0 x 1 x 2 x...x 99 x 100) : (2 + 4 + 6 +...+ 98)
= 0 x : (2 + 4 + 6 +...+ 98)
= 0 x A
= 0
k, (0 + 1 + 2 +...+ 97 + 99) x (45 x 3 - 45 x 2 - 45)
= (0 + 1 + 2 +...+ 97 + 99) x (45 x (3 - 2 - 4))
= (0 + 1 + 2 +...+ 97 + 99) x (45 x 0)
= (0 + 1 + 2 +...+ 97 + 99) x 0
= A x 0
= 0
(15x1-15) x) (10+1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20)
= (15-15) x (10+1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20)
= 0 x (10+1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20)
= 0
= (15 - 15)\(\times\)(10 +1 +2 +3 +4 +5 +6 +7 +8 +9 +10 +11 +12 +13 +14 +15 +16 +17 +18 +19 +20)
= 0\(\times\)(10 +1 +2 +3 +4 +5 +6 +7 +8 +9 +10 +11 +12 +13 +14 +15 +16 +17 +18 +19 +20)
= 0
\(a)\frac{5}{12}+\frac{3}{14}+\frac{7}{12}=\left(\frac{5}{12}+\frac{7}{12}\right)+\frac{3}{4}=1+\frac{3}{4}=\frac{7}{4}\)
\(b)\frac{15}{14}\times\frac{17}{18}\times\frac{28}{15}=\frac{15\times17\times28}{14\times18\times15}=\frac{17}{9}\)
\(c)\frac{5}{8}\times\frac{5}{4}+\frac{5}{4}\times\frac{3}{8}=\frac{5}{4}\times\left(\frac{5}{8}+\frac{3}{8}\right)=\frac{5}{4}\times1=\frac{5}{8}\)
~Học tốt~