Bobby bought 3 5/12 ft of red ribbon and 5 1/12 ft of yellow ribbon. ribbon costs $1.20 a foot. how much did bobby spend on ribbon?

First multiply the big numbers. 3*1.20= ($3.60) and 5*1.20= ($6) 
Now the fractions, 1/12 would equal 10 cents. 5/12 + 1/12= 6/12 which would also equal (60 cents).   3.60+6.00+.60= $10.20