Cheryl can make 3 scarves with the ball of yarn left
Cheryl has used out of the ball of yarn. So the amount of scarves she can make with the yarn has reduced
Yards left = 100 - 10 = 90 yards
Number of scarves she can make with the yards left = yards left / yards needed to crochet a scarf
90 / 30 = 3 scarves
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