A frog lays 800 eggs a year.  10 percent dry up, and 70 percent are eaten.  1/4 of the remaining eggs end up hatching, how many frogs hatch out of the 800?
Dried up:800(.10)=80 eggs
800(.70)=560 eggs
Total left:800-80-560=<<800-80-560=160>>160 eggs
160/4=<<160/4=40>>40 eggs survive to hatch
#### 40