Jim runs 5 miles a day for 30 days for a total of 5*30=<<5*30=150>>150 miles.
The next month Jim runs 10 miles a day for 10*30= <<10*30=300>>300 miles.
The last month Jim runs 20 miles a day for 20*30=<<20*30=600>>600 a month.
All together, Jim runs 150+300+600= <<150+300+600=1050>>1050 miles in three months.
#### 1050