Tính: $-\frac{12}{15} + \frac{4}{26}$

không cần làm hết thanks
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**Bài toán 3: Tính**
a) $-\frac{12}{15} + \frac{4}{26}$
b) $-\frac{1}{21} - \frac{1}{14}$
c) $-\frac{1}{9} + \frac{5}{12}$
d) $\frac{5}{8} - \frac{7}{10}$

**Bài toán 4: Tính**
a) $1 - \left( \frac{1}{12} - \frac{1}{4} \right)$
b) $\frac{3}{7} + \left(-\frac{5}{2}\right) + \left(-\frac{3}{5}\right)$
c) $\frac{4}{5} + \frac{7}{10}$
d) $\frac{2}{5} + \left(-\frac{4}{3}\right) + \left(-\frac{1}{2}\right)$
e) $-\frac{1}{24} \left[ \frac{1}{4} - \left( 1 - \frac{2}{7} \right) \right]$
f) $\left( \frac{5}{7} - \frac{7}{5} \right) - \left[ \frac{1}{2} - \left( \frac{2}{7} + \frac{1}{10} \right) \right]$

**Bài toán 5: Tìm x, bi t:**
a) $x - \frac{1}{5} - \frac{3}{6} = 1$
b) $\frac{16}{5} - x = \frac{4}{5} - \frac{3}{10}$
c) $\frac{1}{20} - \left( x - \frac{8}{5} \right) = \frac{1}{10}$
d) $x + \frac{1}{3} = \frac{2}{5} + \frac{3}{2}$
e) $\left( \frac{3}{8} - \frac{1}{5} \right) \left( \frac{5}{8} - x \right) = \frac{1}{5}$

**Bài toán 6: Tìm x, bi t:**
a) $|x + 1| - \frac{2}{3} = \frac{1}{5}$
b) $|x + \frac{3}{4}| + \frac{1}{3} = \frac{5}{6}$
c) $\frac{9}{2} \left[ \frac{2}{3} - \left( x + \frac{7}{4} \right) \right] = -\frac{5}{4}$
d) $\frac{4}{3} \left( x - \frac{1}{5} \right) = -\frac{3}{10} + \frac{1}{2} - \frac{1}{6}$

**Bài toán 7: Tính:**
a) $\frac{1}{4} + \left| \frac{1}{3} - 5 \left( -\frac{5}{12} \right) + \frac{1}{2} \right|$
b) $3 - \frac{3}{4} + \left| -\frac{1}{10} - \frac{3}{20} \right|$
c) $\frac{3}{4} \left( \frac{12}{8} - \frac{15}{2} + \frac{6}{20} \right)$
d) $-\left| \frac{6}{5} - \frac{1}{2} - \left( \frac{3}{4} - \frac{5}{8} \right) - \frac{3}{2} \right|$

**Bài toán 8: Tính nhanh**
a) $A = \frac{1}{1.2} + \frac{1}{2.3} + \ldots + \frac{1}{2019.2020}$
b) $B = \frac{1}{9.10} + \frac{1}{8.9} + \frac{1}{2.3} + \frac{1}{1.2}$
c) $C = \frac{1}{3.5} + \frac{1}{5.7} + \ldots + \frac{1}{2017.2019}$