1. You flip a nickel, a dime, and a quarter. a) Use a tree diagram to show the number of possible outcomes.

Step 1 ：Create a tree diagram to show the possible outcomes of flipping a nickel, a dime, and a quarter. Each coin has two possible outcomes: heads (H) or tails (T).

Step 2 ：The tree diagram consists of the following possible outcomes: \( \boxed{['NHHH', 'NHHT', 'NHTH', 'NHTT', 'NTHH', 'NTHT', 'NTTH', 'NTTT', 'DHHH', 'DHHT', 'DHTH', 'DHTT', 'DTHH', 'DTHT', 'DTTH', 'DTTT', 'QHHH', 'QHHT', 'QHTH', 'QHTT', 'QTHH', 'QTHT', 'QTTH', 'QTTT']} \)