Danny collects bottle caps. He threw away 31 of the old ones at the park while he found 50 bottle caps new ones. Now he has 310 bottle caps in his collection. How many more bottle caps did danny find at the park than those he threw away?
Danny has 310 bottle caps in his collection. 
He threw away 31 old ones at the park. 
That means he had 341 bottle caps before he went to the park. 
He found 50 new ones at the park. 
That means he had 391 bottle caps at the park. 

So, Danny found 50 more bottle caps at the park than those he threw away.