On monday, deborah ran 3 2/5 miles and on tuesday she ran 4 1/5 miles how many miles did she run on these 2 days togehter

Convert the two fractions into simpler fractions: 3 2/5 - - > 17/5 and 4 1/5 - - > 21/5. Notice the the denominators are identical, so we simply add the numerators: (17 + 21) / 5 = 38/5 = 7 3/5.

There is an easier way to do this, this is just the most clear way of seeing everything.