- Each friend has 10 nails to paint
- There are 8 friends
- Jackie finished painting 4 friend's nails
If there are 8 friends, and each friend has 10 nails to paint, then there are 80 nails that need to be painted in total.
Jackie finished painting 40 nails.
So the math sentence will be:
80 - 40 = 40
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Jackie needs to paint 40 more nails.