A system bet is essentially a fast way of combining a bunch of parlays. Below is an example of a 3/4 system bet, but you can apply what is described to a 4/8 or any other type of system bet.
In a 3/4 bet you are making 4 selections. Let's call the A,B,C,D. The 3/4 means that you are wagering on every 3-team parlay combination avaialable from those 4 selections. So you would be wagering on a,b,c and a,b,d and a,c,d and b,c,d. If you get at least 3 right, you will be paid based on the odds of that particular parlay. You can see that in this scenario if you only get 3 out of the 4 selections right, you will receive some money back, but it is likely that you will lose overall. For example, if you get a,b,c correct you will win 1 out of the 4 possible wagers. The only way to get the maximum amount is to get every selection correct, and then you will be paid out on all 4 possible winning combinations.
The formula for total number of combinations is:
Where n is the number of total selections (4 in our example) and r is the number of picks per parlay (3 in our example)
So in a 4/8 system bet, there are a total of 70 wagers you are making. The amount you are betting on each parlay is your total wager divided by 70. So you can see that if you betting 5 chips on every total, the amount you are wagering on each of the 70 parlays is only .07 chips. Therefore you could get 4,5 or even 6 selections correct, and receive payment back, but depending on the odds you would still lose overall.