Answer:
Find the total number of oranges.
Total oranges = 90 × 5
= 450
Since 1/5 were rotten oranges,
Fraction of oranges that were not rotten
= Fraction of total oranges - Fraction of rotten oranges
= 5/5 - 1/5
= 4/5
Number of oranges not rotten = 4/5 × 450
= 360