Answer:
10 sundaes will be vanilla.
Explanation:
Given:
Fernando is making 30 sundaes with mint, chocolate,and vanilla ice cream.
1/3 of the Sunday's are mint ice-cream.
And 1/2 of the remaining sundaes are chocolate.
The rest are vanilla.
Now, to find the number of sundaes that will be vanilla.
Fernando is making sundaes total = 30.
So, the quantity of sundaes that are mint ice-cream:

Thus, 10 sundaes are mint ice-cream.
So, the remaining sundaes are:

Thus, the remaining sundaes are = 20.
Now, to get the quantity of chocolate sundaes of the remaining sundaes:

Hence, 10 sundaes are chocolate of the remaining 20 sundaes.
As, given the rest are vanilla.
Now, to get the vanilla sundaes we subtract the 10 chocolate ice-cream from the 20 remaining sundaes:

Therefore, 10 sundaes will be vanilla.