Four students can choose to participate in a charity event either on Saturday or Sunday. What’s the probability that there is at least one student at both Saturday's and Sunday's events? A. 1/8

B. 3/8

C. 5/8

D. 7/8

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?