$N^$ is defined as $0.5(N+10)$ for any number $N$ . What is $N$ , if $((N^)^)^=15$ ?

Correct answer marked below

A. 20

B. 30

C. 40

D. 50

Correct

E. 60

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Explanation

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Comments

DangAug 17

Thanks, this one clicked once I just worked backward instead of plugging in every answer choice.

ShinjniAug 31

How did you know to work backward? I always default to testing choices.

VishalAug 26

Wait, is applying the function three times just the same formula with N+something? I got a bit lost on the last step.

YugeshAug 30

I did that at first too and it gave me the wrong answer until I redid it step by step.

PrajwalAug 18

This felt more like a 600-level question once you see the nested function pattern. Took me longer than it should have.

JuliaSep 23

Plugging the choices was surprisingly quick here. Start in the middle and adjust based on whether you land above or below 15.

Victoria6d ago

I did the same but I'd still rather solve it algebraically to be safe.

What this question tests

Your ability to evaluate and compose functions, including unusual defined operations.

Applying function operations in the wrong order or ignoring domain restrictions.

N∗N^*N∗ is defined as 0.5(N+10)0.5(N+10)0.5(N+10) for any number NNN. What is NNN, if ((N∗)∗)∗=15((N^*)^*)^*=15((N∗)∗)∗=15?