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 them 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)
You can use this calculator to view the number of combination outputs.
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 are 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.