Astate health department reports a 55% rate of a certain virus for the "at-risk" population. under certain conditions, a preliminary screening test for the virus is correct 90% of the time. (subjects are not told that they are infected until additional tests verify the results.) if someone is randomly selected from the at-risk population, what is the probability that they have the virus if it is known that they have tested positive in the initial screening?

1. seamount a raised footwall block between normal fault creates this 2. syncline break between rocks where a hanging wall rises relative to a footwall 3. hot spring on rolling hills, this a dip between hills 4. volcanic neck created when a block with hanging walls slips down between normal faults 5. caldera underwater volcano that never reaches above sea level 6. horst natural hot water on earth's surface containing many minerals 7. graben underwater volcano whose top is eroded flat by waves 8. crater less than a mile in diameter; looks like a bowl at the top of a volcano 9. guyot magma that filled the central vent that remains after the volcano has eroded 10. reverse fault over 1 mile in diameter; looks like a bowl over a volcano