Santa wants to deliver presents to every little boy and girl in the whole world. He plans his trip as follows: starting from the North Pole, he travels along a great circle cutting through both poles, ending up back on the North Pole. Next, he turns his path by 1 0 degrees, and travels the great circle, ending up back at the North Pole. He repeats this until he traveled through all the great circles 1 0 degrees apart. If he has to do all of this in 1 2 hours, then the smallest possible integer average speed in km/h for him to make it is N . Find the last three digits of N .
Assume that the Earth is a perfectly spherical 1 2 , 7 4 2 km diameter ball.
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Wouldn't the last three digits be 45 because you have to round the 60,045.2 down?
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Not quite, because if Santa went at 60,045 km/h, he wouldn't be able to deliver all of the presents in time!
The question asks for you to round the speed to the smallest possible value such that Santa is able to complete his mission on time.
one trip around the world is R π . Since he is traveling 1 0 1 8 0 = 1 8 times around the world, because he doesn't want to travel the same path in the different direction. In total that is 1 8 R π . The journey has to finish in 12h, so v = t 1 8 R π = 1 2 h 1 8 × 1 2 7 4 2 K m × π = 6 0 0 4 5 . 2 6 . He mustn't travel slower, and since we are asked the smallest possible integer average that is 6 0 0 4 6
Smallest possible integer average speed = Ceiling(Total Distance Traveled in km / Time taken in hours) = Ceiling(18 π 12742/10) = Ceiling(60045.2604) = 60046 km/h.
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We need to 1st find the Earth's Circumference in accord with the given assumptions. Approximating the value of pie as 2 2 / 7 does not work because of the Earth's Large Diameter. ( I know because I got two tries one with pie as 3 . 1 4 and one with pie as 2 2 / 7 both wrong.) So we use the more accurate value of the Earth's Circumference as π ∗ 1 2 7 4 2 . The amount of great circles we have to traverse is given by 1 8 0 / 1 0 which is 1 8 . Hence our total distance is π ∗ 1 2 7 4 2 ∗ 1 8 . To get speed simply divide it by time giving us ( π ∗ 1 2 7 4 2 ∗ 1 8 ) / 1 2 . Just put these values in Wolfram Alpha to get the final answer which is minimum speed 6 0 , 0 4 5 . 2 . Now enter last three digits after rounding up the value.