Tìm số x trong mỗi tỉ lệ thức sau:

a) $\frac{x}{26} = \frac{21}{39}$

$x \times 39 = 26 \times 21$

x = 14

b) $4 / 5.2 = x / \frac{2}{7}$

$f r a c 1013 = x / f r a c 27$

$x = f r a c 2091$

c)$\frac{1.25}{0.1x}=\frac{1.35}{0.2}

$0.1 x \times 1.35 = 1.25 \times 0.2$

$x = \frac{50}{27}$

d*) $(3 x - 2) / \frac{7}{2} = \frac{4}{21} / \frac{1}{12}$

$(3 x - 2) t i m e s \frac{2}{7} = \frac{4}{21} t i m e s 12$

$\frac{2 (3 x - 2)}{7} = \frac{16}{7}$

2(3x - 2) = 16

$x = \frac{10}{3}$