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Toast Schedule (Posted on 2013-05-13) Difficulty: 3 of 5
Ricardo's old toaster can hold at most two slices of bread and toast them on one side at a time. He wants his bread toasted on both sides and buttered on one side.

It takes:
  • 3 seconds to put each slice into the toaster and,
  • 30 seconds to toast one side of 1 or 2 slices and,
  • 3 seconds to reverse a slice and,
  • 12 seconds to butter one side (that side must already be toasted).
  • 3 seconds to remove a slice from the toaster without putting it back in reverse.
Assuming that, only one of these operations can be done at a time:

In how short a time can Ricardo toast and butter three slices?

No Solution Yet Submitted by K Sengupta    
Rating: 1.3333 (3 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution re: solution Comment 3 of 3 |
(In reply to solution by Charlie)

It would help to remove the slices from the toaster before buttering them.

 1. Load slices A & B into toaster  :  6 seconds.
 2. Toast them                      : 30 
 3. Reverse slice A                 :  3
 4. Remove slice B                  :  3
 5. Place slice C in toaster        :  3
 6. Toast                           : 30
 7. Reverse slice C                 :  3
 8. Remove slice A                  :  3
 9. Reload slice B, opposite side   :  3
10. Toast                           : 30 *
11. Remove slices B & C from toaster:  6
12  Butter each slice               : 36
                                   ---------
                                    156 sec.
(As Steve pointed out, if one was permitted to butter slice A while the other two slices were toasting, the time can be reduced by 12 seconds.)

Edited on May 14, 2013, 2:57 pm
  Posted by Dej Mar on 2013-05-14 14:49:09

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