Math Riddles

 
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Question: The London Racetrack needs to submit its 3 fastest horses to the Kentucky Derby out of 25 horses. However, all of their information was lost and they don't know any of the horse's times. Similarly, they all look identical so they can't remember who's fastest.

They can only race 5 horses at once, so what is the fewest number of races they can conduct to find the 3 fastest horses?

Answer: 7 races are required.

First you divide the 25 horses into 5 groups of 5. You conduct the 5 races and take all of the fastest horses in those races and have a race with them, giving you the fastest horse. Then you take the remaining 24 horses (excluding the fastest) and remove the 4th and 5th horses in the first set of 5 races (since they definitely have 3 horses faster than them), leaving you with 14 horses. Next you can remove all of the horses that were beat in the preliminary race by the horses that got 4th and 5th in the championship race, leaving you with 8 horses. Finally, you can remove the horses that remain that lost to the 3rd place horse in the final race in the preliminary race and the horse that got 3rd in the preliminary to the horse that got 2nd in the championship race, leaving you with 5 horses.

You can then run a final race where the 1st and 2nd place horses are the 2nd and 3rd fastest. Then you know the 3 fastest horses.

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Question: Jasmine has a toaster with two slots that toasts one side of each piece of bread at a time, and it takes one minute to do so.

If she wants to make 3 pieces of toast, what is the least amount of time she needs to toast them on both sides?

Answer: 3 minutes. She puts two pieces in the toaster, toasting one side of each. Then she flips one of them, takes one out, and puts the completely untoasted piece into the toaster. Finally, she takes out the toasted piece and puts the two half-toasted pieces of bread into the toaster for a minute and she's done.

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By IamTHEbest

Question: What is the difference between a dollar and a half and thirty five-cents?

Answer: Nothing. A dollar and a half is the same as thirty five-cents (nickels). But not the same as thirty-five cents.

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Question: Two boys, Trevor and Tyler, are running a 100 meter race. The first time they race Trevor beats Tyler by 5 meters. To make things fair, the next time they race Trevor stands 5 meters behind the starting line.

Who wins the second race (assuming they run the same speed as the first race)?

Answer: Trevor wins again. In the first race Trevor ran 100 meters in the time it took Tyler to run 95 meters. So in the second race when Tyler is at the 95 meter mark Trevor will also be there (since 100 - 5 = 95). Since Trevor is faster he will pass Tyler in the last 5 meters of the race.

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Question: You have 7 tennis balls that are all identical but one of them is slightly lighter than the others.

Using a balance scale and only two separate weightings, how can you find the light tennis ball?

Answer: Put three of the balls on each side. If they are even the ball that wasn't weighed is the light one. If they aren't even the side that is lighter has the light ball. Of these three balls, one should be put on each side. If the sides are even than the other ball is the light one. If they aren't even the one that is lighter is the ball you're looking for.

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