The number of tricks you can establish from your long suit depends on how the distribution lies between the Opps.
If your team has 7 in a suit, as in the example below, you are missing 6 cards. It's often possible that they can be evenly distributed between the Opps :
- 3 - 3 : avec A K Q you'll always make the 4th trick with the 2
- 4 - 2 : You'll never make the 4th trick with the 2
Your team have 10 cards : There are only 3 missing which will drop under the A,K and Q. You will always make 6 ♠ tricks. The 3 honors, then the 9,8 and 7 respectively, giving you a total of 6.