John buys 30 ducks for $10 each.  They weigh 4 pounds and he sells them for $5 per pound.  How much profit did he make?
He bought the ducks for 30*10=$<<30*10=300>>300
He sold each duck for 4*5=$<<4*5=20>>20
So he sold all the ducks for 30*20=$<<30*20=600>>600
So he made a profit of 600-300=$<<600-300=300>>300
#### 300