Question

Kong took 15, percent fewer seconds than Nolan took to complete his multiplication timed test. Kong took 85 seconds.

Answer 1

Kong took 85 seconds to complete his multiplication timed test. Consider the proportion:

Nolan took x seconds - 100%

Kong took 85 seconds - 100%-15%=85%

That is mathematically

$\dfrac{x}{85}=\dfrac{100}{85},\\ \\x=\dfrac{100\cdot 85}{85}=100\ seconds.$

Answer: Nolan took 100 seconds to complete the test.

Answer 2

Nolan took 100 seconds. Is what khan academy says.