Alright! We know that the total number of students is 100%. So, if 65% of the students brought a hot lunch, in order to find how many students brought a packed lunch you subtract it from 100%:
[100 - 65] = 35
So 35% of the students brought a packed lunch. Now, in order to find the fraction of students you simply put 35% of students over the total percent of students (100%)"
[35/100]
Then you simply:
[35/100] ⇒ [7/20]
The answer is 7/20ths of the students brought a packed lunch.
More:
Decimal form - .35
Percentage form - 35%