Starting with FALL, change one letter at a time until you have the word COLD.
Each change leaves the other letters in their original places and must result in a proper word.
What is the minimum number of steps required to achieve this change?
Hint: One way is to change FALL to BALL.
FALL, BALL, BALD, BOLD, COLD
FALL, TALL, TOLL, TOLD, COLD
FALL, MALL, MOLL, MOLD, COLD.