Answer:
3/10 trays of chocolate donuts
Step-by-step explanation:
We know that:
Chocolate donuts = one thirds (1/3) cinnamon donuts
and they sold 9/10 of a tray of cinnamon donuts
=> trays of chocolate donuts = 1/3 trays of cinnamon donuts
= 1/3 * 9/10
= 3/10
So they sold 3/10 trays of chocolate donuts