Jack has a grove with 4 trees by 5 trees.  It takes 6 minutes to clean each tree.  He gets help to clean the trees so it only takes half as long.  How many hours did he spend cleaning trees?
There were 4*5=<<4*5=20>>20 trees to clean
So it took 20*6=<<20*6=120>>120 minutes
That is 120/60=<<120/60=2>>2 hours
So he spent 2/2=<<2/2=1>>1 hour cleaning
#### 1