1. Which of the expressions below has a sum of 0? Select all that apply. A) -18 + 81
B) -12 + 12
C) -6 + 6
D) 12 + (-21)
E) 3.3 + (-3.3)

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step-by-step explanation:

in counting the number of heads in 4 coin flips, the probability that we get exactly one head is the probability that we get anyone of the following 4 outcomes: httt, thtt, ttht, or ttth. each has probability 1/16, so the probability to get exactly one head in 4 flips is 1/16 + 1/16 + 1/16 + 1/16 = 4/16 = 1/4.