If K percent of K percent of 4000 = 90, then what is the value of K?
2021
If K percent of K percent of 4000 = 90, then what is the value of K?
- A.
15
- B.
30
- C.
7.5
- D.
22.5
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Correct answer: A
Solution: Let K percent of K percent of 4000 equal 90 and solve for K.
Write the expression: (K/100) × (K/100) × 4000 = (K^2/10000) × 4000 which simplifies to 0.4·K^2.
Set equal to 90 and solve:
0.4·K^2 = 90
K^2 = 90 / 0.4 = 225
K = √225 = 15 (reject negative root because percent is nonnegative)
Check: (15/100)^2×4000 = 0.0225×4000 = 90, so K = 15 is correct.