Key concept: Percent of a part vs. percent of the whole
The classic mistake here: students read "40 toys were found defective" and "20% were not identified," then calculate 20% of 40 = 8 and add it, getting 48. Then 48/200 = 24% and pick B. The issue? Those 40 are already a subset — the identified defectives. The 20% unidentified is a fraction of the total defective count, not of the 40.
Step 1 — Define the variable correctly.
Let x = total number of defective toys.
Step 2 — Translate the key sentence.
"40 toys were found defective. However, 20% of the defective toys were not identified."
→ The identified ones = 80% of all defectives = 40
→ 0.8x = 40
Step 3 — Solve.
x = 40 / 0.8 = 50
Step 4 — Find the percentage.
50 out of 200 total toys = 50/200 = 25%
Answer: C
Takeaway: Whenever a word problem gives you a subset but asks about the whole, always define the unknown as the total and work backwards — don't let the given number anchor you into treating it as the base.