If the students aren't familiar with the concept of Jumble, I give them a quick example. The first example on this worksheet is fine. You could write "ufro" on the board and ask the students "What number is this?" If they're confused, write "four" beneath it and draw arrows between the letters showing that they've been mixed up.
After that, pass out the worksheet and ask the students to fill out the rest of the numbers. You might want to have them do one through ten first, then check the answers as a class by writing them on the blackboard. You'll find that some students are much quicker than others. Speed is no issue. The important thing is to practice spelling!
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