Pierre is running 26 and 2/10 miles in the marathon. he has run 3/4 of the way. how far has he run?

Pierre ran 19 and 13/20 miles.

Given:
marathon length : 26 2/10 miles
pierre's length ran : 3/4 of the way.

Multiply the fractions. 
Convert the marathon length from a mixed fraction into a fraction.
26 2/10 = ((26*10)+2)/10 = (260+2)/10 = 262/10

262/10 * 3/4 = (262*3) / (10*4) = 786/40 = 19 26/40

19 26/40 simplified to 19 13/20 miles

26 ÷ 2 = 13
40 ÷ 2 = 20