Mike was going to sell all of his stamp collection to buy a video game. After selling half of them he changed his mind. He then bought ten more. How many did he start with if he now has 27?

Answser:

34

Step-by-step explanation:

think of it as this:

s - (s/2) + 10=27

s symbolizes the amount of stamps mike has, now begin to evaluate, (doing the opposite operations to the solution) subtract the 10 from itself and the 10 from the 27

s - (s/2) + 10=27

-10 - 10

0 17

now you have

s - (s/2) = 17

now just multiply 17 by 2 and you get your answer of 34