Josh had 19 marbles in his collection. He lost 11 marbles and found 5 new ones. How many marbles does he have now?
Let's denote the number of marbles Josh had in his collection by m. Then we have 

m=19. 

Josh lost 11 marbles, so we have 

m-11=8. 

Josh found 5 new marbles, so we have 

m+5=13. 

Therefore the answer (numeric) is: 

13-8=5