Since he receives four pairs of pants every year, and a pair has two pants, he gets 4*2 = <<4*2=8>>8 pants every year.
After five years, the total number of pants he'll receive is 5*8 = <<5*8=40>>40 pants.
If he initially had 50 pants, he'll have a total of 50+40 = <<50+40=90>>90 pants in five years.
#### 90