If f(x) = k(x - k) and k is a constant, what is the value of f(4) - f(3), in terms of k? - The Beat The GMAT Forum

If f(x) = k(x - k) and k is a constant, what is the value of f(4) - f(3), in terms of k?

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BTGModeratorVI: Legendary Member; Posts: 1223; Joined: Sat Feb 15, 2020 2:23 pmFollowed by: 1 member

by BTGModeratorVI » Mon Sep 14, 2020 8:33 am

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If f(x) = k(x - k) and k is a constant, what is the value of f(4) - f(3), in terms of k?

(A) 1
(B) k
(C) 7k - 1
(D) k^2 + k
(E) k^2 - k

Answer: B
Source: GMAT hacks

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Source: Beat The GMAT — Problem Solving | Mon Sep 14, 2020 8:33 am

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

Re: If f(x) = k(x - k) and k is a constant, what is the value of f(4) - f(3), in terms of k?

by Brent@GMATPrepNow » Sat Sep 19, 2020 6:06 am

BTGModeratorVI wrote: ↑
Mon Sep 14, 2020 8:33 am
If f(x) = k(x - k) and k is a constant, what is the value of f(4) - f(3), in terms of k?

(A) 1
(B) k
(C) 7k - 1
(D) k^2 + k
(E) k^2 - k

Answer: B
Source: GMAT hacks

Given: f(x) = k(x - k)
So, for example, f(9) = k(9 - k) = 9k - k²

The question asks for the value of f(4) - f(3)
f(4) - f(3) = [k(4 - k)] - [k(3 - k)]
= [4k - k²] - [3k - k²]
= k

Answer: B

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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