The Answer is = 1.2 hours
Work Step by Step
#1 To find out how many problems Carlos did you multiply the number of hours he worked by 25, to find out how many problems Cecelia did you multiply the number of hours she worked by 30. Because Carlos started 12 mins early he will have completed 5 problems by the time Cecelia starts ($12\div60$ $\times 25$) to find out how long it will take them to have completed the same number of problems we from the equation 25x = 30x - 5 #2 Solve for x 25x = 30x -5 -30x , -30x -5x = -5 $-5x \div$ -5 =$-5 \div-5$ x = 1 #3 x is the numbers of hours after Cecelia starts that they will have done the same amount of problems, so you need to add the 12 min head start that Carlos had. x + .2 (.2 for 12 minutes ) 1 + .2 = 1.2 hours.