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Brian's school locker has a three-digit combination lock that can be set using the numbers 5 to 9 (including 5 and 9), without repeating a number. the probability that the locker code begins with a prime number is %. the probability that the last digit of the locker code is an odd number is %.

Some gamma ray bursts are hypothesized to come from mergers of neutron stars or black holes. if this hypothesis is correct, what else should we in principle be able to detect from such mergers? a. gravitiational waves b. x-ray bursts c. significant disruption of gas thousands of light-years away in the surrounding galaxy d. an "afterglow" of bright visible light, lasting for weeks

One disadvantage that darwin faces today is w. enemy attacks x. natural disasters y. lack of land bridge z. high population density