Elvis makes 5 squares with 4 matchsticks each for a total of 5*4 = <<5*4=20>>20 matchsticks
Ralph makes 3 squares with 8 matchsticks each for a total of 8*3 = <<3*8=24>>24 matchsticks
They used a total of 20+24 = <<20+24=44>>44 matchsticks
There will be 50-44 = <<50-44=6>>6 matchsticks left in the box
#### 6