There are 30 students in Ms. Leech's class. Twice as many girls as boys are in the class. There are 10 boys in the class and each boy today brought 5 cups for science activity class as Ms. Leech had instructed. If the total number of cups brought by the students in the class is 90, how many cups did each girl bring? Think carefully first, then make a decision:
If there are 30 students in Ms. Leech's class, and the number of boys is 10, the number of girls in Ms. Leech class is 30 - 10 = 20. If each boy brought 5 cups for the science activity, the total number of cups brought by the boys is 5 * 10 = 50 cups. The number of cups that the girls brought is 90 - 50 = 40 of the total number. Since the number of girls in the class is 20, each girl brought 40 / 20 = 2 cups each. So, the answer is 2.