How many ways are there to arrange (3) mobile covers from (6) different mobile covers on a shop shelf in order?

Correct answer: 120

Since the order of covers on the shelf matters, use permutations. There are 6 choices for the first position, 5 for the second, and 4 for the third. Thus, the total number of arrangements is \({}^{6}P_{3}=6\times5\times4=120\). The value 60 is \({}^{6}C_{3}\), which applies when order does not matter. Exam tip: Use permutations for ordered placements in a row or on a shelf.