13. Решите пропорции: 3:1,5=4:x 3:19=2:0,8x

Решение:

1. \( 3:1,5 = 4:x \)

\( 3 \cdot x = 1,5 \cdot 4 \)

\( 3x = 6 \)

\( x = \frac{6}{3} \)

\( x = 2 \)

2. \( 3:19 = 2:0,8x \)

\( 3 \cdot 0,8x = 19 \cdot 2 \)

\( 2,4x = 38 \)

\( x = \frac{38}{2,4} = \frac{380}{24} = \frac{95}{6} \)

Ответ: 1. \( x = 2 \); 2. \( x = \frac{95}{6} \).