Andrew is having two of his friends over for a sleepover. For one friend, Brian, he asks his mother to buy 3 donuts. He asks for his other friend, Samuel, to get the same. A day before the sleepover Andrew ends up inviting two more friends and asks his mother to buy them the same amount of donuts. Just in case, Andrew's mother wants to buy one more donut for each of Andrew's friends. Andrew's mother is going to buy the same amount of donuts for Andrew as everybody else. How many donuts will Andrew's mother need to buy?
Thoughts? Step-by-step reasoning:
Andrew is having 4 friends over who will get 3 donuts each, 4 x 3 = 12 donuts total. Andrew's mother wants to get 1 extra donut for each of Andrew's friends, 3 donuts + 1 extra = 4 donuts for each of Andrew's friends. Andrew's mother is buying 12 + 4 extra donuts for Andrew's friends = 16 total donuts. Andrew's mother is also going to get 3 + 1 extra donut for Andrew = 4 donuts. Andrew's mother will need to buy 16 donuts for Andrew's friends + 4 donuts for Andrew = 20 total donuts.
Thus, the answer is 20.