Give the step-by-step reasoning process and then the final answer. Angel has written letters to all of her pen pals and is putting all of the letters in envelopes. Most of the letters are put into large envelopes and the remaining 20 letters are put into small envelopes. The large envelopes each contain 2 letters each. If Angel has written a total of 80 letters, how many large envelopes did she use?
As some of the letters are in small envelopes, there must be 80 total letters – 20 letters in small envelopes = 60 letters in large envelopes. Angel therefore used 60 letters / 2 letters per large envelope = 30 large envelopes.
The final answer: 30.