Should you buy the 4 and 10 instead of placing them?
Yes. Buying the 4 and 10 costs far less than placing them, especially where the 5% commission is charged only on wins. Keep placing the 6 and 8.
On the 4 or 10: place 6.67%; buy with the commission on wins only 1.67%; buy with the commission paid up front 4.76%.
Place or buy, number by number
| Number | Place | Buy, commission on wins | Buy, commission up front |
|---|---|---|---|
| 4 | 6.67% | 1.67% | 4.76% |
| 5 | 4.00% | 2.00% | 4.76% |
| 6 | 1.52% | 2.27% | 4.76% |
| 8 | 1.52% | 2.27% | 4.76% |
| 9 | 4.00% | 2.00% | 4.76% |
| 10 | 6.67% | 1.67% | 4.76% |
House edge per bet decided, with a 5% commission. Up front, the commission is paid when the bet is made and counts as money bet.
Why
A place bet on the 4 or 10 pays 9 to 5 against true odds of 2 to 1, which is a big shortfall. A buy bet pays the true 2 to 1 and charges a 5% commission instead. If the commission is taken only when the bet wins, you pay it on a third of your decisions. On the 6 and 8 the place payout of 7 to 6 is already close to true odds, so buying them costs more than placing them.