If Judy did not make any contribution her taxable income (assuming no other deductions) will be $60,000, on which she will pay tax of $9,967 (plus a further $1,200 for the 2% Medicare Levy).
However when she makes a $20,000 superannuation contribution her taxable income reduces by $20,000, saving her $5,825 in personal tax (and $400 on the Medicare Levy).
However, the super contribution will attract contributions tax of 15% in the fund, being $3,000. Therefore the overall tax saving in this scenario is $2,825 (being $5,825 less $3,000). There is also an additional $400 saving on the Medicare Levy. The balance of the concessional contribution of $17,000 will form part of the taxable component of Judy’s super account and further tax could be payable when withdrawn (if she is under age 60 at the time or it is paid to any non-tax dependants upon her death).