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![](https://rs.olm.vn/images/avt/0.png?1311)
3.75 : \(\dfrac{1}{4}\) + 3.75 : 0.5 + 3,75 + \(\dfrac{1}{8}\) + 3,75 x 86
= 3,75 : \(\left(\dfrac{1}{4}+0.5+\dfrac{1}{8}\right)\) + 3,75 x 86
= 3,75 : \(\dfrac{7}{8}\) + 322.5
= 4,3 + 322.5 = 326,8
tích hộ chị nha
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a,=\frac{7-1}{1.3.7}+\frac{9-3}{3.7.9}+\frac{13-7}{7.9.13}+\frac{15-9}{9.13.15}\)\(+\frac{19-13}{13.15.19}\)
\(=\frac{1}{1.3}-\frac{1}{3.7}+\frac{1}{3.7}-\frac{1}{7.9}+\frac{1}{7.9}-\frac{1}{9.13}+\frac{1}{9.13}-\frac{1}{13.15}+\frac{1}{13.15}-\frac{1}{15.19}\)
\(=\frac{1}{1.3}-\frac{1}{15.19}=\frac{95}{285}-\frac{1}{285}=\frac{94}{285}\)
\(b,=\frac{1}{6}.\left(\frac{6}{1.3.7}+\frac{6}{3.7.9}+\frac{6}{7.9.13}+\frac{6}{9.13.15}+\frac{6}{13.15.19}\right)\)
làm giống như trên
\(c,=\frac{1}{8}.\left(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{48.49.50}\right)\)
\(=\frac{1}{16}.\left(\frac{2}{1.2.3}+\frac{2}{2.3.4}+\frac{2}{3.4.5}+...+\frac{2}{48.49.50}\right)\)
\(=\frac{1}{16}.\left(\frac{3-1}{1.2.3}+\frac{4-2}{2.3.4}+\frac{5-3}{3.4.5}+...+\frac{50-48}{48.49.50}\right)\)
\(=\frac{1}{16}.\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+\frac{1}{3.4}-\frac{1}{4.5}+...+\frac{1}{48.49}-\frac{1}{49.50}\right)\)
\(=\frac{1}{16}.\left(\frac{1}{2}-\frac{1}{2450}\right)=\frac{1}{16}.\left(\frac{1225}{2450}-\frac{1}{2450}\right)=\frac{153}{4900}\)
\(d,=\frac{5}{7}.\left(\frac{7}{1.5.8}+\frac{7}{5.8.12}+\frac{7}{8.12.15}+...+\frac{7}{33.36.40}\right)\)
\(=\frac{5}{7}.\left(\frac{8-1}{1.5.8}+\frac{12-5}{5.8.12}+\frac{15-8}{8.12.15}+...+\frac{40-33}{33.36.40}\right)\)
\(=\frac{5}{7}.\left(\frac{1}{1.5}-\frac{1}{5.8}+\frac{1}{5.8}-\frac{1}{8.12}+\frac{1}{8.12}-\frac{1}{12.15}+...+\frac{1}{33.36}-\frac{1}{36.40}\right)\)
\(=\frac{5}{7}.\left(\frac{1}{5}-\frac{1}{1440}\right)=\frac{5}{7}.\left(\frac{288}{1440}-\frac{1}{1440}\right)=\frac{41}{288}\)
P/S: . là nhân nha
![](https://rs.olm.vn/images/avt/0.png?1311)
1/3xD=1/(2x4)+1/(4x6)+...+1/(98x100)
2/3xD=2/(2x4)+2/(4x6)+...+1/(98x100)
2/3xD= 1/2-1/4+1/4-1/6+...+1/98-1/100
2/3xD=1/2-1/100
2/3xD=49/100
D=147/200
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài giải
\(\frac{2}{3}+\frac{3}{4}+\frac{4}{5}=\frac{40}{60}+\frac{45}{60}+\frac{48}{60}=\frac{133}{60}\)
\(\frac{8}{5}+\frac{7}{6}+\frac{10}{9}+\frac{1}{2}=\frac{144}{90}+\frac{105}{90}+\frac{100}{90}+\frac{45}{90}=\frac{394}{90}\)
\(\frac{15}{17}-\frac{11}{13}+\frac{3}{26}=\frac{390}{442}+\frac{374}{442}+\frac{51}{442}=\frac{815}{442}\)
\(\frac{9}{12}\text{ x }\frac{4}{3}\text{ : }\frac{8}{5}=\frac{9}{12}\text{ x }\frac{4}{3}\text{ x }\frac{5}{8}=\frac{9\text{ x }4\text{ x }5}{12\text{ x }3\text{ x }8}=\frac{5}{8}\)
\(\frac{4}{5}\text{ x }\frac{15}{8}\text{ : }\frac{5}{7}=\frac{4}{5}\text{ x }\frac{15}{8}\text{ x }\frac{7}{5}=\frac{4\text{ x }15\text{ x }7}{5\text{ x }8\text{ x }5}=\frac{21}{10}\)
\(\frac{2}{3}+\frac{3}{4}+\frac{4}{5}=\frac{40}{60}+\frac{45}{60}+\frac{48}{60}=\frac{133}{60}\)
\(\frac{8}{5}+\frac{7}{6}+\frac{10}{9}+\frac{1}{2}=\frac{144}{90}+\frac{105}{90}+\frac{100}{90}+\frac{45}{90}=\frac{197}{45}\)
\(\frac{15}{17}-\frac{11}{13}+\frac{1}{26}=\frac{390}{442}+\frac{374}{442}+\frac{51}{442}=\frac{815}{442}\)
\(\frac{9}{12}\times\frac{4}{3}:\frac{8}{5}=1:\frac{8}{5}=\frac{5}{8}\)
\(\frac{4}{5}\times\frac{15}{8}:\frac{5}{7}=\frac{3}{2}:\frac{5}{7}=\frac{21}{10}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+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 +30
= 20x9 +30
=180+30
=210
tk cho mik nhé
![](https://rs.olm.vn/images/avt/0.png?1311)
a)x*4/5:2=6/7 b)6/5:x:5/4=10/15
x*4/5=6/7 x 2 6/5:x=10/15 x 5/4
x*4/5=12/7 6/5:x=5/6
x=12/7:4/5 x=6/5:5/6
x=15/7 x=36/25
a) x * 4/5 : 2 = 6/7
x * 4/5 = 6/7 *2
x *4/5 = 12/7
x = 12/7 : 4/5
x = 15/7
Vậy x = 15/7
a) C1: 8/15 : 4/5 + 7/15 : 4/5 C2: 8/15 : 4/5 + 7/15 : 4/5
= (8/15 + 7/15) :4/5 = 2/3 + 7/12
= 1 : 4/5 =5/4
= 5/4
b) C1: (5,8 + 4,7) : 0,25 C2: (5,8 + 4,7) : 0,25
= 10,5 : 0,25 = 5,8 : 0,25 + 4,7 : 0,25
= 42 = 23,2 + 18,8
= 42
c)C1: (7/3 - 2/3) : 4/9 C2: (7/3 - 2/3) : 4/9
= 5/3 : 4/9 = 7/3 : 4/9 - 2/3 : 4/9
= 15/4 = 21/4 - 3/2
= 15/4
d) C1: 0,08 : 0,16 - 0,04 : 0,16 C2: 0,08 : 0,16 - 0,04 : 0,16
= 1/2 - 1/4 = (0,08 - 0,04) : 0,16
= 1/4 = 0,04 : 0,16
=1/4
Nhớ k mình nha