Which (if any) of these intervals is it possible to measure given two sand timers (which change from question to question)? There are no minute marks, halfway points, etc.
A. 7 minutes with 4- and 5-minute timers
B. 15 minutes with 7- and 11-minute timers
C. 14 minutes with 5- and 8-minute timers
If one (or more) is possible, specify how it can be done with the given timers.