Question 698476
you can factor out x to get 


3x+2x = (3+2)x 


then you add 3 and 2 to get 5 to get



3x+2x = (3+2)x = (5)x = 5x


So that's why 3x+2x = 5x


You can think of it as "I have 3 x-rays and I get 2 more x-rays. I will have 5 total x-rays"