Len walks 3/10 mile in the morning. He walks 2/5 mile in the afternoon to a friends house. Len says that he walks a total of 5/15 mile in the morning and afternoon

No he walks 7/10 of a mile

you have to make 2/5 have a common denominator with 3/10

so 2*2=4 (numerator)

2*5=10 (denominator)

4/10+3/10 = 7/10

since you only add the numerator because the denominator makes it a like term