If you want to throw a birthday party to your friends, which of the following can be useful data?
1, 3 & 5
1 & 3
Last name, height and weight of your friends are of course not relevant for planning the party. But according to the number of your friends, you will get snacks, arrange for space. Also, if you know the amount expected to be spent on each friend, you can ask sufficient money from your dad.