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?

(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