An athlete runs R miles in H hours, then rides a bicycle Q miles in the same number of hours. Which of the following represents the athlete's average speed, in miles per hour, for these two activities combined?
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A$${R-Q}\over{H}$$
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B$${R-Q}\over{2H}$$
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C$$2{(R+Q)}\over{H}$$
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D$$2{(R+Q)}\over{2H}$$
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E$${R+Q}\over{2H}$$