The present ages of Sohail, Afzal and Bilal are 17 years, 16 years and 12 years respectively. If the age of Aslam is also included, the average age of the group increases by 5 years. What is the present age, in years, of Aslam?

Introduction / Context:
This problem is about how the average age of a group changes when a new member is added. It is common in quantitative aptitude sections dealing with averages and age based questions. The key point is to understand how total age and number of persons interact to produce the average, and how to reverse engineer the unknown age of a newly added person from the change in average.

Given Data / Assumptions:

• Present ages are 17 years for Sohail, 16 years for Afzal and 12 years for Bilal.
• When Aslam age is included, the average age of the group increases by 5 years compared to the average of the first three.
• We must find the present age of Aslam.
• All ages are in years and considered positive.

Concept / Approach:
First, we compute the average age of the initial three people. Then, using the given information that the new average with four people is 5 years more, we compute the new average. Multiplying each average by the number of people gives the total of their ages. The difference between the total for four people and the total for three people must be the age of Aslam. This is a standard application of the formula average = total sum divided by number of items.

Step-by-Step Solution:
Step 1: Compute the total age of Sohail, Afzal and Bilal: 17 + 16 + 12 = 45 years. Step 2: Find the average age of these three individuals: 45 / 3 = 15 years. Step 3: When Aslam is included, the average age increases by 5 years, so the new average becomes 15 + 5 = 20 years. Step 4: With Aslam added, there are now 4 people in the group. Step 5: The total age of all four people is new average * number of people = 20 * 4 = 80 years. Step 6: The total age of the first three was 45 years, so the age of Aslam is 80 - 45 = 35 years. Step 7: Therefore, Aslam present age is 35 years.

Verification / Alternative check:
We can verify by checking the average with the calculated age. If Aslam is 35 years old, the four ages are 17, 16, 12 and 35. Their sum is 17 + 16 + 12 + 35 = 80 years. The average is 80 / 4 = 20 years. This is exactly 5 years more than the original average of 15 years that we calculated for the first three. The conditions are satisfied, confirming that 35 years is the correct age for Aslam.

Why Other Options Are Wrong:
Option A (32 years) would produce a total of 45 + 32 = 77 years, giving an average of 77 / 4 which is less than 20, so the increase of 5 years would not hold.
Option B (33 years) leads to a total of 78 and an average of 19.5 years, again not an increase of exactly 5 years.
Option C (34 years) gives a total of 79 years, with an average of 19.75 years, which still does not match the required new average of 20 years.

Common Pitfalls:
Students sometimes mistakenly add 5 years to each individual age instead of interpreting it as a change in the average. Another common mistake is to forget to multiply the average by the correct number of people when reconstructing the total. Always remember that the total sum is the average multiplied by the number of items, and small arithmetic errors in this step can lead to wrong answers.

Final Answer:
The present age of Aslam is 35 years.