A lucky 31 consists of 31 possible bet combinations involving selections in 5 different events.  
The bets include 5 singles, 10 doubles, 10 trebles, 5 fourfolds and an accumulator.
 
A single is a selection of just 1 event, a double is a combination of 2 events, treble is a combination of 3 events, a four-fold is a combination of 4 events and an accumulator in this instance means a combination of all 5 events.
 
E.g You place a lucky 31 bet on games A,B, C, D and E.
Let's say your stake is N50, please note that your total stake will be 50 X 31 = 1550
This is so because your stake is charged separately for each possible combination and winnings are credited for each correct combination as well.
 
Your combinations would be arranged thus:
5 singles
A X 50 = Winnings
B X 50 = Winnings
C X 50 = Winnings
D X 50 = Winnings
E X 50 = Winnings
 
10 doubles
A*B X 50 = Winnings 
A*C X 50 = Winnings
A*D X 50 = Winnings
A*E X 50 = Winnings
B*C X 50 = Winnings
B*D X 50 = Winnings
B*E X 50 = Winnings
C*D X 50 = Winnings
C*E X 50 = Winnings
D*E X 50 = Winnings
 
10 Trebles
A*B*C X 50 = Winnings
A*B*D X 50 = Winnings
A*B*E X 50 = Winnings
A*C*D X 50 = Winnings
A*C*E X 50 = Winnings
A*D*E X 50 = Winnings
B*C*D X 50 = Winnings
B*C*E X 50 = Winnings
B*D*E X 50 = Winnings
C*D*E X 50 = Winnings
 
5 Four-Folds
A*B*C*D X 50 = Winnings
A*C*D*E X 50 = Winnings
A*B*D*E X 50 = Winnings
B*C*D*E X 50 = Winnings
A*B*C*E X 50 = Winnings
 
Accumulator
A*B*C*D*E X 50 = Winnings
If only one selection wins, returns are paid to double the odds.
 
An example of a lucky 31 bet is displayed in the attached picture