Question

help me bài 1,2

**Bài 1:**

Thực hiện phép tính (tính hợp lý nếu có thể)

a) \( \frac{5}{13} + \frac{2}{7} + \frac{8}{13} - \frac{3}{14} \)

b) \( \frac{5}{22} - \frac{3}{4} + \frac{5}{21} + \frac{19}{22} \)

c) \( \frac{3}{17} + \frac{1}{9} + \frac{14}{17} - \frac{2}{3} \)

d) \( \frac{-7}{8} - \frac{3}{19} + \frac{5}{6} + \frac{-7}{8} + \frac{16}{19} \)

**Bài 2:**

Tìm \( x \), biết:

a) \( \frac{3}{7} \cdot x = -\frac{1}{3} - \frac{2}{9} \)

b) \( \frac{3}{11} \cdot x - \frac{11}{3} = \frac{-3}{22} \)

c) \( \frac{1}{5} \cdot x + \frac{1}{2} = \frac{1}{3} + \frac{2}{5} \)

d) \( \frac{2}{5} \cdot x + \frac{1}{3} \cdot x = \frac{2}{3} \)

Answer 1

Bài 1:

a: \(\frac{5}{13}+\frac27+\frac{8}{13}-\frac{3}{14}\)

\(=\left(\frac{5}{13}+\frac{8}{13}\right)+\frac27-\frac{3}{14}\)

\(=\frac{13}{13}+\frac{4}{14}-\frac{3}{14}=1+\frac{1}{14}=\frac{15}{14}\)

b: \(\frac{5}{21}\cdot\frac{-3}{22}-\frac{-4}{21}+\frac{5}{21}\cdot\frac{-19}{22}\)

\(=\frac{5}{21}\left(-\frac{3}{22}-\frac{19}{22}\right)+\frac{4}{21}\)

\(=\frac{5}{21}\cdot\frac{-22}{22}+\frac{4}{21}=\frac{-5}{21}+\frac{4}{21}=-\frac{1}{21}\)

c: \(\frac{3}{17}+\frac19+\frac{14}{17}-\frac23\)

\(=\left(\frac{3}{17}+\frac{14}{17}\right)+\left(\frac19-\frac23\right)\)

\(=1+\frac19-\frac69=1-\frac59=\frac49\)

d: \(-\frac78\cdot\frac{3}{19}-\frac56+\frac{-7}{8}\cdot\frac{16}{19}\)

\(=-\frac78\left(\frac{3}{19}+\frac{16}{19}\right)-\frac56\)

\(=-\frac78-\frac56=-\frac{21}{24}-\frac{20}{24}=-\frac{41}{24}\)

Bài 4:

Thời gian kể từ lúc Việt xuất phát đến lúc hai xe gặp nhau là:

7h30p-6h50p=40p=2/3(giờ)

Thời gian kể từ lúc Nam xuất phát đến lúc hai xe gặp nhau là:

7h30p-7h10p=20p=1/3(giờ)

Độ dài quãng đường AB là:

\(15\cdot\frac23+12\cdot\frac13=10+4=14\left(\operatorname{km}\right)\)

Bài 2:

a: \(\frac37x=-\frac13:\frac29\)

=>\(\frac37x=-\frac13\cdot\frac92=-\frac32\)

=>\(x=-\frac32:\frac37=-\frac72\)

b: \(\frac{3}{11}:x-1\frac{1}{11}=-\frac{3}{22}\)

=>\(\frac{3}{11}:x=-\frac{3}{22}+\frac{12}{11}=-\frac{3}{22}+\frac{24}{22}=\frac{21}{22}\)

=>\(x=\frac{3}{11}:\frac{21}{22}=\frac{3}{11}\cdot\frac{22}{21}=\frac27\)

c: \(\frac15:x+\frac12=\frac13+\frac25\)

=>\(\frac15:x=\frac13+\frac25-\frac12=\frac25-\frac16=\frac{7}{30}\)

=>\(x=\frac15:\frac{7}{30}=\frac15\cdot\frac{30}{7}=\frac67\)

d: Ta có: \(\frac25x+\frac13x=\frac23\)

=>\(x\left(\frac25+\frac13\right)=\frac23\)

=>\(x\left(\frac{6}{15}+\frac{5}{15}\right)=\frac23\)

=>\(x\cdot\frac{11}{15}=\frac23\)

=>\(x=\frac23:\frac{11}{15}=\frac23\cdot\frac{15}{11}=\frac{2\cdot5}{11}=\frac{10}{11}\)