Solve the Fraction Division: 3/10 ÷ x = 1/2

To solve this problem, we'll expression the division problem as an equation:

$\frac{3}{10} \div x = \frac{1}{2}$

This can be rewritten using multiplication:

$\frac{3}{10} \times \frac{1}{x} = \frac{1}{2}$

To solve for $x$, cross-multiply to clear the fractions:

$3 \times 2 = 10 \times 1 \times x$

$6 = 10x$

Solve for $x$ by dividing both sides by 10:

$x = \frac{6}{10} = \frac{3}{5}$

Therefore, the missing number is $\frac{3}{5}$, which corresponds to choice 3.