School disco

This practical task is about working out patterns with numbers.
disco ball and disco dance floor
Practical Task
 
The cost to get into a school disco is $2. If you want to buy a can of drink at the disco it costs $1. 

a)  How much will it cost if you go to the disco and buy one drink? $_____

b)  What is the total cost for 2 sisters to go to the disco and buy a drink each? $_____

c)  What is the total cost for 3 friends to go to the disco and buy a drink each? $_____

 

The teacher gives the correct answers to a), b), and c) at this point, if a mistake has been made.
 
 
d)  Without using the coins, what is the total cost of 10 people going to the disco and each buying a drink? 
 
      $__________
 
e)  How did you work this out?