Daania had green and yellow marbles for sale. She sold 120 green marbles. 25% of the marbles sold were yellow. How many marbles did Daania sell altogether?

1. Determine the percentage of green marbles sold

Since $25\%$ of the marbles sold were yellow, the percentage of green marbles sold is:
$100\% - 25\% = 75\%$

2. Find the total number of marbles sold

We know that $75\%$ of the marbles sold corresponds to $120$ green marbles.
$75\% \rightarrow 120$
$1\% \rightarrow \frac{120}{75} = 1.6$
$100\% \rightarrow 1.6 \times 100 = 160$

Alternatively, using fractions:
$75\% = \frac{3}{4}$
$\frac{3}{4}$ of total $= 120$
$\frac{1}{4}$ of total $= 120 \div 3 = 40$
Total $= 40 \times 4 = 160$