For a certain integer x, the units digit of (x+2)^2 is 9. Which of the

Question

For a certain integer x, the units digit of (x+2)^2 is 9. Which of the following could be the units digit of |x+1|?

A. 0
B. 3
C. 4
D. 5
E. 7

JeffTargetTestPrep · Accepted Answer

The only way to get a units digit of 9 when squaring an integer is for the original integer to have a units digit of 3 or 7. Thus, since (x+2)^2 has a units digit of 9, x could be 1, 5,-5, or -9. Let’s plug each value into |x + 1|.

When x = 1, |x + 1| = 2, which is not an answer choice.

When x = 5, |x + 1| = 6, which is not an answer choice.

When x = -5, |x + 1| = |-4| = 4, which IS an answer choice.

When x = -9, |x + 1| = |-8| = 8, which is not an answer choice.

Answer: C

Abhishek009 · Answer

(x+2)^2 = 9

So, Units digit of (x+2) will be 3 or 7

Thus, the units digit of x can be either 1 or 5

Units digit of |x+1| must be 4 or 6

Among the given option only (C) is possible, hence this is our answer...

dorane · Answer

I'll bet my uncle's beer-can collection it's C; i.e., x = -5, -15, etc.

Funsho84 · Answer

X= -5

-5 + 1 = -4
Absolute value = 4

Answer: c

matthewsmith_89 · Answer

x could be 5 or 1.
If x is one, then we get a result of 4. Therefore the answer is C.

KrishnakumarKA1 · Answer

if the unit digit of square of the number is 9, the unit digit will be either 3 or 7 if x is positive and 5 and 9 if x is negative 
hence the unit digit of x will be either 1 or 5 if x is positive and 5 and 9 if x is negative 
hence |x+1| will yield the unit digit as 2 or 6 if x is positive and 4 and 8 if x is negative.

looking at the option we can see that 4 is the only option

Option C

SeregaP · Answer

(x+2)^2=9
it's supposed to end 3 or 7

I tried negative numbers: -5+3=-3^2=9
|-5+1|=4

guptarahul · Answer

A. 0
B. 3
 C. 4 
D. 5
E. 7

Unit digit on squaring any number can be 9 if and only if unit number of which we are squaring, must be either 3 or 7

And to have 7 or 3 at unit digit x can be 1,5,-5,-9

When x = 1, |x + 1| = 2,

When x = 5, |x + 1| = 6,

When x = -5, |x + 1| = |-4| = 4,

When x = -9, |x + 1| = |-8| = 8,

KanishkM · Answer

Key word : certain integer x

(x+2)^2 is 9

x= -9 or x = -5 or x = 5 or x = 1

Only value which is present after using the above values in |x+1|

4

C

shashwat91 · Answer

(x+2)^2 = 9, means --> last digit of x must be -5,(-5+2=3)
|x+1|--> _/(x+1)^2 or, x+1-->therefore last digit 4 (|-5+1|=4)

geezus24x7 · Answer

Solution to this problem has already been discussed in detail. Just want to add another slightly different approach to select from the available options-

Unit digit of (x+2)^2 is 9, so x has to be an odd number and therefore |x+1| has to be an even number, which is only one of the available option, i.e. 4

sarahel · Answer

(x+2)^2 = units digit 9
x + 2 is odd 
so x has to odd
and x+1 has to be even
answer is either A or C
If A was true then x+1 = units digit 0 x would be 9 ->(9+2)^2= 11^2 = units digit 1 not 9 . A not the answer
C is correct

CEdward · Answer

There are only two single-digit #s that when squared will give you 9, irrespective of the value of the tens digit onwards: 3 and 7
3^2 = 9
7^2 = 9

Therefore, try different values for x that would result in the contents inside the parantheses being equal to 3,-3,7, or -7.

x = 1 --> (1 + 2)^2 = 9 ------> | 1 + 1 | = 2 NO
x = -5 --> ( -5 +2) ^2 = 49 -----> | -5 + 1 | = 4 YES

Answer is C.

Kinshook · Answer

Given: For a certain integer x, the units digit of (x+2)^2 is 9.
Asked: Which of the following could be the units digit of |x+1|?

Unit digit of |x+2| = 3 or 7
Unit digit of x+2 = {3,-3,7,-7}
Unit digit of x+1 = {2,-4,6,-8}
Unit digit of |x+1| = {2,4,6,8}

IMO C

lnyngayan · Answer

By solving |x+2| = 3 or -3, I understand why x could be 1 and -5.
But wonder why x could be 5 or -9 too?

Bunuel · Answer

Check the highlighted part.

The unit's digit of |x+2| can also be 7.

findingmyself · Answer

Try Plugging in some single-digit and 2-digit numbers for X

X=1
X=5
X=-7

None of the answer choices are coming up.

Now try 
X=-15
X=11

When using -15, we will get an answer as 4 
There is no logic I am using as such, But the only insight is that there is no mention of positive and negative integer. Hence I am taking worst case scenarios.

For a certain integer x, the units digit of (x+2)^2 is 9. Which of the

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GMAT Problem Solving (PS) Questions

For a certain integer x, the units digit of (x+2)^2 is 9. Which of the

Prep Toolkit

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

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My Rewards