T minus 27 hours a problem occurred. If not fixed by T minus 8 hours, the launch will be scratched. How much time to fix the problem?

Question

A countdown for a space shuttle has occurred. At "T minus 27 hours" (that is, 27 hours before launch) a problem occurs. If the technicians have not fixed the problem before T minus 8 hours, the launch will have to be scratched. How much time do the technicians have to correct the problem?

Answer 1

This problem can be easily understood if you draw a number line.  Mark the launch time as “T” and count ticks to the left to mark “T-27” and “T-8.”

 

The amount of time to correct the problem is:

          (T-8) – (T-27) hours

           T – 8 – T + 27 hours                    [distribute the (-1)]

              19 hours 

 

(notes to help in estimating:  If the technicians have 27 hours before launch and they take 20 hours of it, that puts them 7 hours before launch.  Adjust that for 27 and 19 to get 8 hours.)