a) 5, 3, 4, 2
Numerele de 4 cifre care se pot forma sunt:
2345, 2354, 2435, 2453, 2534, 2543, 3245, 3254, 3425, 3452, 3524, 3542, 4235, 4253, 4325, 4352, 4523, 4532, 5432, 5423, 5324, 5342, 5234, 5243.
b)
Numerele obținute la punctul a), ordonate:
crescător: 2345, 2354, 2435, 2453, 2534, 2543, 3245, 3254, 3425, 3452, 3524, 3542, 4235, 4253, 4325, 4352, 4523, 4532, 5234, 5243, 5324, 5342, 5423, 5432.
descrescător: 5432, 5423, 5342, 5324, 5243, 5234, 4532, 4523, 4352, 4325, 4253, 4235, 3542, 3524, 3452, 3425, 3254, 3245, 2543, 2534, 2453, 2435, 2354, 2345.