99,999^2 - 1^2 =?

[seanceserene]

99,999^2 - 1^2 =?

A. 10^10 - 2
B. (10^5 - 2)^2
C. 10^4(10^5 - 2)
D. 10^5(10^4 - 2)
E. 10^5(10^5 - 2)


i am going to take the exam tomorrow, please help with this tricky one
thanks in advance

[neoreaves]

ok first of all best of luck ...just relax when you take the exam ...gmat only tests a few concepts but it tricks you so you cant use them


like in this question all you need to know is

x^2 -1 = (x+1)(x-1)

so 99999^2 - 1^2 = (99999 + 1) (99999 - 1) = 10^5(10^5-2)

So the answer should be E

[pops]

99,999^2 - 1^2 =?

A. 10^10 - 2
B. (10^5 - 2)^2
C. 10^4(10^5 - 2)
D. 10^5(10^4 - 2)
E. 10^5(10^5 - 2)


i am going to take the exam tomorrow, please help with this tricky one
thanks in advance

Lots of Good Luck and Good Wishes to you !!

Rather than the answer to your problem, you should remember these formulae:
a^2-b^2=(a+b)(a-b)
(a+b)^2=a^2+b^2+2ab
(a-b)^2=a^2+b^2-2ab
a^3-b^3=(a-b)(a^2+b^2+ab)
a^3+b^3=(a+b)(a^2+b^2-ab)

[seanceserene]

ok first of all best of luck ...just relax when you take the exam ...gmat only tests a few concepts but it tricks you so you cant use them


like in this question all you need to know is

x^2 -1 = (x+1)(x-1)

so 99999^2 - 1^2 = (99999 + 1) (99999 - 1) = 10^5(10^5-2)

So the answer should be E

OMG, i mistook the "," for dot.
i thought it is nighty-nine point nine nine nine, which injects me despair
thank you..

[Scott@TargetTestPrep]

99,999^2 - 1^2 =?

A. 10^10 - 2
B. (10^5 - 2)^2
C. 10^4(10^5 - 2)
D. 10^5(10^4 - 2)
E. 10^5(10^5 - 2)

Using the difference of squares, we have:

(99,999 + 1)(99,999 - 1)

(100,000)(99,998)

(100,000)(100,000 - 2)

10^5(10^5 - 2)

Answer: E