Nidhi brings 42 muffins to a bake sale. She only uses trays for groups of 10 muffins. Each plate holds only 1 muffin. How many trays could Nidhi use to display the muffins?

The correct answer is: 4

Nidhi has 42 muffins: 42 is 4 tens and 2 ones.
Nidhi puts 1 ten(10) muffins in one tray. She has 4 tens muffins.
Hence, Nidhi uses 4 trays to display the muffins.