Class ranking change: A class has 45 students and a boy is ranked 20th from the top. Two boys join, and his rank drops by one place. What is his new rank from the bottom?

Introduction / Context:
When class size changes, relative ranks can shift. Here, two students join and the given student drops by one from the top. We are to compute his rank from the bottom after the change.

Given Data / Assumptions:

• Initial size = 45; boy's top-rank = 20.
• Two new boys join ⇒ new size = 47.
• His rank “drops by one” from the top ⇒ new top-rank = 21.

Concept / Approach:
Rank-from-bottom after change is computed by: bottom-rank = N − top-rank + 1 with the new N and the new top-rank.

Step-by-Step Solution:

Verification / Alternative check:
Counting positions: if he is 21st from top in 47, then 26 stand below him, making his bottom-rank 26 + 1 = 27.

Why Other Options Are Wrong:

• 25th, 26th, 28th: Each assumes an incorrect conversion or class size.
• None of these: The correct answer is present.

Common Pitfalls:
Forgetting to use the new class size (47) or ignoring the “drops by one” detail.

Final Answer:
27th