For all positive integers x, f(x)=f(x+1). If f(3)=15, then what is f(7

Question

For all positive integers x, f(x)=f(x+1). If f(3)=15, then what is f(7)?

A. 8
B. 12
C. 15
D. 21
E. 35

Kudos for a correct  solution .

Bunuel · Accepted Answer

VERITAS PREP OFFICIAL SOLUTION:

This problem really just comes down to understanding the function notation. If f(x)=f(x+1), that means that:

f(3)=f(3+1)=f(4)
and that

f(4)=f(4+1)=f(5)
and so on, meaning that really all functions equal the same thing as the next function up, so all functions are equal. That means that f(7) is the same thing as f(3), which we're told is 15. Therefore the answer is 15.

chetan2u · Answer

ans C... all values of x should be the same ie 15.. unless i am missing something here

sunita123 · Answer

f(x)=f(x+1)
f(3)=15
=>f(3)=f(3+1)=f(4)=f(4+1)=f(5)=f(5+1)=f(6)=f(6+1)=f(7)=15

so Answer is C

DesiGmat · Answer

Here we go---

f(x) = f(x+1) ---(1)

f(3) = 15 ----(2)

Now

f(7) = f(6+1)-----> f(6) = f(5+1)-------> f(5) = f(4+1) ------> f(4) = F(3+1)---> f(3) = 15

Now backtrack
f(4) = 15-----> f(5) = 15 ------> f(6) = 15 ----> f(7) = 15

Though I picked option C

I am still not 100% sure of the answer(don't know why)

My bets on C.

zerosleep · Answer

It is given that: f(x) = f(x+1) implying,
for any value of x, f(x) and f(x +1) has same value => this function is a constant value function.
so for tis function, f(1) = f(2) = f(3) = .... = f(7) = ... f (n-1) = f(n) = 15.
Hence, Ans is (C).

PareshGmat · Answer

f(3) = f(4) = f(5) = f(6) = f(7) = 15

Answer = C

salaxzar · Answer

f(x) = f(x+1) means, 
for any x, f(x) and f(x +1) has same value
so f(1) = f(2) = f(3) = f(x) = f(x+1)= 15.
Hence, Ans is (C).

gurmukh · Answer

F(3)=f(4)= F(5)=f(6)=f(7)=15

Posted from my mobile device

bumpbot · Answer

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For all positive integers x, f(x)=f(x+1). If f(3)=15, then what is f(7

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GMAT Problem Solving (PS) Questions

For all positive integers x, f(x)=f(x+1). If f(3)=15, then what is f(7

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

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My Rewards