From the question
A computer was on sale for 2/4 of the original price
We are given
Original price = $900
We are to find the sale price
With the given information
Sale price = 2/4 of the original price
That is
Sale price = 2/4 of $900
This gives
[tex]\begin{gathered} \text{Sale price }=\frac{2}{4}\times900 \\ \text{Sale price }=\frac{1800}{4} \\ \text{Sale price }=450 \end{gathered}[/tex]