The fraction of students that went to the movies is 14/112. To find the number of students who went to the movies from a larger group, you have to find a fraction equal to 14/112, whose denominator is 2600 (the number of students from the larger group).
14/112 = x/2600
You can do cross multiplication here. Cross multiplication is multiplying the denominator of one fraction by the numerator of the fraction equivalent to it. That product will be equal to the numerator of the first fraction * denominator of the second fraction.
112*x = 14*2600
x = 325
Approximately 325 students out of 2600 students would've gone to the movie last weekend.
