Effect of disease prevalence on predictive values

Consider a population of 2000 people and a diagnostic test that is 90% sensitive and specific. The positive and negative predictive values of the test vary when the prevalence of the disease is varied.
(A) If the prevalence of the disease is high at 50%, the positive and negative predictive values will be similar to the sensitivity and specificity (90%, respectively).
(B) In contrast, if the prevalence of the disease is only 10%, the positive predictive value decreases (50%) and the negative predictive value increases (99%).