Each day, steve walked 1/12 mile more than the previous day. the first day he walked 1/12, the second day he walked 2/12 mile, the third day he walked 3/12 mile. on which day did the sum of his walks total at least 1 complete mule?

1st  day                 = 1/12
2nd day                 =  2/12
3rd  day                =  3/12
4th day                 =   4/12
5th day                 =   5/12
6th day        would be = 6/12

If it continues in that order, the sum of the walks would total 1 mile when:

They all add up to 12/12

Add =       1/12 + 2/12 + 3/12 + 4/12 = 10/12

That is still not up to 12/12

So we add up the 5th day also =    10/12 + 5/12 = 15/12  =  1 3/12  miles

So on the 5th day the sum of his walks total at least 1 completed mile.

At least 1 means 1 and above.  As you can see the answer we got 1 3/12 is already more than 1.