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I'm assuming limit. Correct odds on the flop to see the turn card with a 4 flush is 4:1. This is also the same to see the river card.
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Not quite right. Odds on the flop (4.2:1 w/ 47 cards remaining) are slightly worse than on the turn (4.1:1 w/ 46 cards remaining).
Here is a link to a nice table from poster
LostWages.
Also, the most
practical advice for folding a 4-flush in limit hold'em is DON'T. In almost all cases, you will have pot odds/implied odds to see the river. The board and action has to be very scary to let it go.