It would only be possible if the Book market was set at 100% or less.
This sometimes happens on Betfair, but only for a fraction of a second.

The TAB market is 118% so its not possible unless one weeded out 1 or more runners whose combined price is 18% or less .
e.g. $5.50 horse is approx 18.18%
So take out 1 or more $5.50 horses & your bet book % is now close to 100% So as to break even.
That is if the $5.50 shots dont get up to win.

Remember that one can only break even backing the whole field, if the book percentage is 100% or less.
One would stagger the bets depending on each horses price , for those who dont already know, this is known as Dutching..

Cheers

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Cheers.