The 50% was the target in the two priority of Broadmeadows and Keilor Downs, and not the full 10 suburbs.
With the 10 suburbs though they opened up testing to anyone and not just those with symptoms. But yes they wanted to test many people in all ten suburbs.
Just on the numbers. Let us do the maths. They wanted to do 25,000 tests per day for 10 days (note is now upto 26,000 per day but early on was more like 20K) = 250,000 tests. At 1 in 2, total = 500,000 people.
2016 Census (so will be more now)
Population of Broadmeadows is 11,970
Population of Keilor Downs is 9,995
50% = 11,000 in these two suburbs.
Allow for population increase to 2020. Say 15,000 for those two suburbs. That allows 235,000 tests to do other tests for anyone symptomatic in the rest of Victoria and also to reach 50% later (ie after 3 days) in the other suburbs.
Given that they have kept finding cases in Broadmeadows and Keilor Downs you would imagine that they will want go above 50% there.
They are now also into the 11th day of the blitz and they are clearly continuing with it. So high testing will remaining fora while yet.
Numbers are here:
Live tracking of coronavirus cases, active, tests, deaths, ICU, hospitalisations and vaccinations in Victoria
covidlive.com.au