He gave 3/3=<<3/3=1>>1 box away
So he has 3-1=<<3-1=2>>2 boxes
So he got 2*20=<<2*20=40>>40 burritos
He ate 3*10=<<3*10=30>>30 burritos
So he has 40-30=<<40-30=10>>10 burritos left
#### 10