In an elementary school classroom, two students are given the task of cleaning the chalkboard. The first student can clean it by
himself in one minute, while the other student takes 20 seconds longer. Which of the following equations can be used to determine how many seconds it would take for both students to clean the chalkboard if they work together?
All you do is add them all together... 20 + 11.4 + 11.4 + 4.5 + 4.5 + 0.45 + 0.45 + 0.45 + 0.45 = 53.6Kg (note that 0.45 is 450g in Kg, When adding things such as weight or length you want to make sure that they are all in the same unit)
