These cards are meant to be used as a “fishbowl” exercise. That is, each group is designed to elicit certain types of thinking, and your students should do problems from each group.
You’ll notice that each group features problems where students have to determine one of the three types of solutions: total elapsed time, starting time and ending time. This is by design: they should know how to do all three (that is, if you believe the Common Core propaganda machine, which I don’t, but I have to....)
The “A” problems all use “even” numbers - that is, the intervals are by 5s, which is great for your weaker students who need some practice using “easier” numbers to solve the problems. They also stay “within” the hour, as well as go “over” the hour, so they can get used to this type of problem.
The “B” problems feature one number that is not “even,” but the other number is. This is a step up from the previous problems, in that your students can “step” to an even number on either the beginning of the task or at the end. For example, one problem has an elapsed time of 12 minutes, ending at 10:00. This is designed so that your students can count back 10 minutes and then 2 minutes to 9:48 (or they can counting back 2 minutes then 10 minutes; either way is fine.)
The “C” problems use uneven numbers in both clues: they can choose a range of strategies to solve it, which may be skip counting by 10s and then compensating (for example, counting up 50 minutes from 6:12, then adding 3 more minutes, or just recognizing that that 53 minutes later is 7 minutes less than an hour - they may say “6:12 + 1 hour = 7:12, then go back 7 minutes to 6:05.”
The “D” cards are very mischievous, because they will almost force your kids to use compensation: if you add 59 minutes to a time, then it’s much easier to skip an hour and move back a minute than add 59 minutes, no?
I’ve also included a sheet of “blank” cards where you or your students can make their own problems to share with one another. Please have them do this! One of the little known aspects of the CCSS is its emphasis on higher levels of cognitive thought, and designing and sharing problems that are created by students is one way to reach these “higher levels.” Believe me, you won’t find it in your enVision, Go Math! or other textbooks; it wasn’t included.
Finally, I included large versions of some of the task cards for your to use in whole class discussions with your students. There’s also a blank one, so you can create your own or have your students make a “problem of the day which they can share with one another.”