Okay, here we have this:
Considering the provided information, we are going to calculate the requested value, so we obtain the following:
Then we will substitute in the following formula:
Students who play soccer=Number of students*(Probability that they play soccer)
Replacing:
Students who play soccer=300*(12/25)
Students who play soccer=3600/25
Students who play soccer=144
Finally we obtain that 144 students would we expect to play soccer, based on Sean's experiment.
You can solve by subtracting: 500-330
but I like to use mental math and think this way:
she has 330
70 more will give her 400
and 100 more will give her 500
100 + 70 is 170.