More context would be helpful.
A flip here almost certainly refers to a coin flip. Normally, a fair coin flip would be 50-50 (50% heads, 50% tails).
A 7-5 flip would be a coin that lands heads 7 times and lands tails 5 times (58%/42%).
The text appears to say that Buffet will invest larger than expected amounts of money when the odds are slightly favorable (58%).
Buffet has a reputation for making large percentages (100% 300%) on his investments. It is very unlikely that he is looking to invest five units to get two (put five in, get seven out).