The Eleven Keys

Wording of this Handout:

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UNDOORALSOAPSPYREAMENDS

Here are eleven keys.

One of them unlocks the treasure chest. To find out which key it is, first work out how many FOUR LETTER WORDS there are in the secret word.
(Reading from left to right- i.e. UNDO, etc)

1 2 3 4 5 6 7 8 9 10 11

The answer is key number_____