P(<100) = P((new or change) & <100) = P(new & <100) + P(change & <100)
... = P(<100 | new)*P(new) + P(<100 | change)*P(change)
... = 0.90*0.70 + 0.20*0.30
... = 0.63 + 0.06 = 0.69 . . . . probability of completing a transaction in < 100 ms
For this you would do

Because 60% is the same as 0.60. And solving a problem like this is the opposite of finding a percent of a number. When you solve this you get 80. So there are 80 students in total.
Answer:
54÷9 = 6 so for the second box is 6 hot dogs per person
54÷27= 2 third box is 2 hot dogs per person
54÷54= 1 fourth box is 1 hot dog per person