A car travels at 10 miles per hour (mph) for one hour, doubles its speed in the second hour, and so on. If it continues to vary its speed like this, by the seventh hour it will be traveling at:
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3200 mph
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1280 mph
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640 mph
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320 mph
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256 mph
Try to solve it before checking the answer.
640 mph
1st hour: 10 mph
2nd hour: \(10 \times 2 = 20 \) mph
3rd hour: \(
(10 \times 2) \times 2 = 10 \times 2^2 \) mph
4th hour: \(
(10 \times 2^2) \times 2 = 10 \times 2^3 \) mph
…
7th hour: \(
10 \times 2^6
\, \frac{Km}{h}
= \boldsymbol{640} \) mph