Lesson: Strange Operators

Rate this video: 
5

Comment on Strange Operators

If xθy=(x+1)/(y−1) for all y≠1, and aθb=1, then a=

A. b−2
B. b−1
C. b
D. b+1
E. b+2

I did (a+1)/(b-1) = 1
I don't understand what should I do to take out a
Thanks in advance
gmat-admin's picture

Let's take it from (a+1)/(b-1) = 1
Multiply both sides of the equation by (b-1) to get: (a+1) = 1(b-1)
Expand right side: a + 1 = b - 1
Subtract 1 from both sides: a = b - 2

Answer: A

Hi Brent, for the below question I am getting the different answer zero, here's why:
(√5 + √5)² - (√5 - √5)² = using the property a² - b² = (a+b)(a-b) I got, (√5 + √5) (√5 - √5) = (2√5)(0) = 0


If x ¤ y = (x + y)² - (x - y)². Then √5 ¤ √5 =

A. 0
B. 5
C. 10
D. 15
E. 20
gmat-admin's picture

Question link: https://gmatclub.com/forum/if-x-y-x-y-x-y-then-218476.html

You made a small mistake in your solution.

You're using the property that says a² - b² = (a + b)(a - b)

So, in the expression, (√5 + √5)² - (√5 - √5)², what is a, and what is b?
Well, a = (√5 + √5) and b = (√5 - √5)

This means (a + b)(a - b) = [(√5 + √5) + (√5 - √5)][(√5 + √5) - (√5 - √5)]
= [(√5 + √5) + 0][(√5 + √5) - 0]
= (√5 + √5)(√5 + √5)
= (2√5)(2√5)
= 4√25
= 20

I have two different solutions posted here: https://gmatclub.com/forum/if-x-y-x-y-x-y-then-218476.html#p1727422

Does that help?

Cheers,
Brent

Add a comment

Ask on Beat The GMAT

If you have any questions, ask them on the Beat The GMAT discussion forums. The average response time is typically less than 30 minutes.

Change Playback Speed

You have the option of watching our videos at various speeds (25% faster, 50% faster, etc). To change the playback speed, click the settings icon on the right side of the video status bar.

Have a question about this video?

Post your question in the Comment section below, and we’ll answer it as fast as humanly possible.

Free “Question of the Day” emails!