Interview Puzzles :: Discussion
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The Old car of Mary requires tires to be changed after each 24000 km. If she wants to go for 42000 km journey then how many minimum numbers of tires she will need?
Explanation :
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she'll need at least 7 tires.
All 7 tires will be used for exactly their max of 24,000 miles.
We know that 4 tires will definitely be used for 24,000 miles since you need four tires for a normal car to work properly.
Now we need to get an extra 18,000 miles to reach 42,000.
3 additional tires will each give 24,000 for a total 72,000 miles. BUT, this will have to be spread over the 4 tire places.
72,000/4 = 18,000 additional miles
Now it's just a matter of rotating the tires in a circle every 6,000 miles. (42,000mi/7tires)
A - B - C - D - E - F - G
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6 6 6 6
12 12 12 6
18 18 12 6
24 18 12 6
12 24 18 12
18 18 24 18
24 24 24 24