Question

Kyra observed that 85% of the students at a library liked reading mystery stories. If 30 students at the library did not like reading mystery stories, the number of students at the library who liked mystery stories was _____. (only put numeric values, no other symbols)

Answer 1

First  calculate that numeric value. It cannot be done immediately without calculations.

if 85% of studends liked mystery that means that 100% - 85% = 15% didnt like.

Those 15% are 30 that were given in text. Now we can calculate this using proportion:

15%        30 students
85%         x students

we use cross multiplication:
15*x = 30*85
x = 30*85/15
x = 170

Answer is 170