The number of cheese slices used to make the ham sandwiches is 10 * 2 = <<10*2=20>>20 cheese slices.
The number of cheese slices used to make the grilled cheese sandwiches is 50 - 20 = <<50-20=30>>30 cheese slices.
The number of grilled cheese sandwiches she makes is 30 / 3 = <<30/3=10>>10 grilled cheese sandwiches.
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