Maria has constructed a rectangular fence, with a perimeter of 200 ft, around her backyard swimming pool. If the width of the enclosure is 60 ft
how many feet is the length?
? ft

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.