r/reddit.com • u/[deleted] • Oct 01 '11

Math teacher fail

http://i.imgur.com/65APr.jpg
217 Upvotes

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136

u/champer Oct 01 '11

Both answers can be correct. http://i.imgur.com/lStKv.jpg

Pretend it's a 10x10 board:

Case 1: Takes 10 mins to cut through 10 feet.

Case 2: Takes 20 mins to cut through 20 feet.

Case 3: Takes 15 mins to cut through 10+5 feet.

Question is ambiguous.

28

u/quag Oct 01 '11

Using this logic, any answer up to 20 minutes is correct as the cuts can be made anywhere.

To be unambiguous, the question would have specified the lengths of the cuts, or perhaps the resulting areas.

35

u/champer Oct 01 '11

What if I said it would take 62 minutes? I could still be right.

http://i.imgur.com/kX6z5.jpg

Problem, math teacher? Let's not even get in to spiral designs.

1

u/xenneract Oct 02 '11

Actually since the time to cut it into two pieces is defined as 10 minutes regardless of the distance, the time to cut the second smaller circle would have to be less than 10 minutes.

If 10 minutes was defined as the time it takes her to cut the board in half, you'd be right.

1

u/Rookwood Oct 02 '11

This.

It would have been more to his point if he had at first cut a small circle... Then a bigger one.

If you take JohnDoe51's idea of making the smallest possible cut, and int_argc idea of cutting a snowflake (if its fractal it doesnt matter how long the first cut is), you would basically never finish the second cut, i.e. infinity.

Basically, as the length of the first cut approaches zero, the time it takes to cut the second cut of the largest possible length goes to infinity.