Step 1: From statement I, the ratio of the present ages of P and Q is 3:4. Let the present ages of P and Q be \( 3x \) and \( 4x \), respectively.
Step 2: From statement II, the ratio of the present ages of Q and R is 4:5. Let the present ages of Q and R be \( 4y \) and \( 5y \), respectively.
Step 3: We have two variables \( x \) and \( y \), and no further relationship is provided between \( x \) and \( y \). Therefore, we cannot determine the ratio of P’s and Q’s ages four years ago with the information given in both statements. Thus, the answer is \( \boxed{{C}} \).
Based upon the results of regular medical check-ups in a hospital, it was found that out of 1000 people, 700 were very healthy, 200 maintained average health and 100 had a poor health record.
Let \( A_1 \): People with good health,
\( A_2 \): People with average health,
and \( A_3 \): People with poor health.
During a pandemic, the data expressed that the chances of people contracting the disease from category \( A_1, A_2 \) and \( A_3 \) are 25%, 35% and 50%, respectively.
Based upon the above information, answer the following questions:
(i) A person was tested randomly. What is the probability that he/she has contracted the disease?}
(ii) Given that the person has not contracted the disease, what is the probability that the person is from category \( A_2 \)?