A teacher observes that if Lisa and Ian work independently
on the same problem, Lisa has a 90% chance of solving the
problem and lan has a 70% chance of solving it. What is
the probability that at least one of them solves the problem?
A 0.97
B 0.63
C 0.2
D 1

Scores on a university exam are normally distributed with a mean of 78 and a standard deviation of 8. the professor teaching the class declares that a score of 70 or higher is required for a grade of at least “c.” using the 68-95-99.7 rule, what percentage of students failed to earn a grade of at least “c”?