The probability is 1/2 that a certain coin will turn up heads on any given toss. If the coin is to be tossed three times, what is the probability that on at least one of the tosses the coin will turn up tails?
Options:
(A) 1/8
(B) 1/2
(C) 3/4
(D) 7/8
(E) 15/16
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P(at last 1 tails) = 1 - P(all heads) = 1 - (1/2)^3 = 7/8. So the answer is: (D).
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A and B together can do a work in 6 days. If A alone can do it in 15 days. In how many days can B alone do it?
Options:
(A) 7
(B) 13
(C) 19
(D) 10
(E) None
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1/6 1/15 = 1/10
B can do the work in 10 days So the answer is: (D).
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A light has a rating of 80 watts, it is replaced with a new light that has 25% higher wattage. How many watts does the new light have?
Options:
(A) 105
(B) 95
(C) 80
(D) 60
(E) 100
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Final number = Initial number + 25%(original number) = 80 + 25%(80) = 80 + 20 = 100. So the answer is: (E).
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