In a school there are 200 students in total.\nIf one-fifth (1/5) of the students are boys, how many students in the school are girls?

Introduction / Context:
This problem combines simple fractions with counting students in a school. Questions like this are very common in aptitude and school level exams because they test whether you can correctly interpret fractional information (like one fifth) and translate it into counts of boys and girls. It also reinforces the idea that the total must be split consistently between the given categories.

Given Data / Assumptions:

• Total number of students in the school = 200.
• One fifth (1/5) of the students are boys.
• The remaining students are girls.
• We assume all students are either boys or girls, with no other categories mentioned.
• We need to find only the number of girls.

Concept / Approach:
First, convert the fraction 1/5 into an actual number of boys by multiplying it with the total number of students. Then, subtract the number of boys from the total to get the number of girls. This approach is straightforward: Number of boys = (1/5) * total. Number of girls = total - number of boys. Understanding such fraction based splits is foundational for more complex ratio and percentage problems.

Step-by-Step Solution:
Step 1: Total students = 200. Step 2: Fraction of students who are boys = 1/5. Step 3: Number of boys = (1/5) * 200. Step 4: Compute 200 / 5 = 40, so there are 40 boys. Step 5: Number of girls = total students - number of boys = 200 - 40. Step 6: Therefore, number of girls = 160.

Verification / Alternative check:
Check whether the distribution is reasonable. If there are 40 boys and 160 girls, then boys form 40 / 200 = 1/5 of the students, and girls form 160 / 200 = 4/5 of the students. The fractions 1/5 and 4/5 add up to 1, confirming that the entire school population is correctly accounted for and that the calculation is consistent.

Why Other Options Are Wrong:
16: This is one fifth of 80, not 200, and is far too small for the given total.

140: Would mean 60 boys (since 200 - 140 = 60), which is 3/10 of the total, not 1/5.

40: This is the number of boys, not the number of girls.

120: Would imply 80 boys (200 - 120), yielding a boy fraction of 80 / 200 = 2/5, not 1/5.

Common Pitfalls:
A common error is to misread 1/5 as 5 or 20%, or to incorrectly think that 1/5 of 200 is 20. Another mistake is to treat 1/5 as if it were the number of girls instead of boys. Carefully identify which part of the population the fraction refers to and double check by adding the calculated parts to ensure they match the total.

Final Answer:
The number of girls in the school is 160.