On monday, he ran 5/6 mile and on tueday, he ran 7/8 mile. The distance that he ran over the two days is
5/6 + 7/8
Lowest common multiple of the denominators, 6 and 8 is 24. Multiplying each term by the denominator, it becomes
(5 * 4) + (3 * 1)/24
= (20 + 21)/24 = 41/24
= 1 17/24 miles