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# Given that p is a positive even integer with a positive

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VP
Joined: 14 May 2006
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Given that p is a positive even integer with a positive  [#permalink]

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Updated on: 29 Sep 2013, 08:47
1
15
00:00

Difficulty:

55% (hard)

Question Stats:

64% (01:39) correct 36% (01:51) wrong based on 516 sessions

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Given that p is a positive even integer with a positive units digit, if the units digit of p^3 minus the units digit of p^2 is equal to 0, what is the units digit of p + 3?

A. 3
B. 6
C. 7
D. 9
E. It cannot be determined from the given information.

Originally posted by u2lover on 08 Aug 2006, 12:59.
Last edited by Bunuel on 29 Sep 2013, 08:47, edited 1 time in total.
Renamed the topic, edited the question and added the OA.
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Given that p is a positive even integer with a positive  [#permalink]

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29 Sep 2013, 08:57
3
2
u2lover wrote:
Given that p is a positive even integer with a positive units digit, if the units digit of p^3 minus the units digit of p^2 is equal to 0, what is the units digit of p + 3?

A. 3
B. 6
C. 7
D. 9
E. It cannot be determined from the given information.

p is a positive even integer with a positive units digit --> the units digit of p can be 2, 4, 6, or 8 --> only options C and E are left.

In order the units digit of p^3 - p^2 to be 0, the units digit of p^3 and p^2 must be the same. Thus the units digit of p can be 0, 1, 5 or 6.

Intersection of values is 6, thus the units digit of p + 3 is 6 + 3 = 9.

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08 Aug 2006, 13:15
1
A

Let x is the unit digit of p. Then

Unit digit of p^3 = unit digit of x^3
Unit digit of p^2 = unit digit of x^2

Their difference is 0 (As given). This is possible only if unit digit is 1 or 0. But since p is an even integer. So unit digit of p =0
hence unit digit of p+3 = 3
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08 Aug 2006, 13:15
Should this be E?

(Unit digit of p^3) - (Unit digit of p^2) = 0 if the units digit is 0, 1, 5, 6.

The answer in these cases would be 3, 4, 8, 9.

Even if 0 is neither posive or negative, we still have 3 options left.

However, only 9 is mentioned from among these choices, so could be D as well... any suggestions?
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08 Aug 2006, 13:24
E It cannot be determined from the given information.

As p is even,
p = 10x+y

y = {0,2,4,6,8}

Unit's digit of p^3 = {0, 4, 6}
Unit's digit of p^2 = {0,2,4, 6, 8}

As unit's digit p^3 -unit's digit p^2 =0

Common units digit between p^3 and p^2 = {0, 4,6}

We can get {0,4,6} in p^2 or p^3 from {0,2,4,6,8}

So cannot determine.
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08 Aug 2006, 13:30
2
ps_dahiya wrote:
A

Let x is the unit digit of p. Then

Unit digit of p^3 = unit digit of x^3
Unit digit of p^2 = unit digit of x^2

Their difference is 0 (As given). This is possible only if unit digit is 1 or 0. But since p is an even integer. So unit digit of p =0
hence unit digit of p+3 = 3

What the heck I was thinking

Answer should be D because last digit of p must be +ve and even.
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08 Aug 2006, 13:42
u2lover wrote:
Given that p is a positive even integer with a positive units digit, if the units digit of p^3 minus the units digit of p^2 is equal to 0, what is the units digit of p + 3?

A 3
B 6
C 7
D 9
E It cannot be determined from the given information.

unit digits could be 0, 1, 5 and 6 but only 6 satisfies the conditions given in the question. so D make sense..
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Joined: 26 Jun 2006
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08 Aug 2006, 14:46
1
From the condition,

p is even and not divisible by 10 (because units digits is positive)

so p=2k, and k can not be multiple of 5 or 10

p^3-p^2 = p^2(p-1) = (2k)^2*(2k-1)

Since we know that units digit of p^3-p^2 is 0 and k con not be 5 or 10,
the only way to get 0 at the end of the number is if 2k-1=5

=> 2k=6 => p=6 => p+3=9

(D)
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09 Aug 2006, 16:03
Hey U2...
Can you tell me where I missed this question?

My solution is below... goes without saying got it wrong...

haas_mba07 wrote:
E It cannot be determined from the given information.

As p is even,
p = 10x+y

y = {0,2,4,6,8}

Unit's digit of p^3 = {0, 4, 6}
Unit's digit of p^2 = {0,2,4, 6, 8}

As unit's digit p^3 -unit's digit p^2 =0

Common units digit between p^3 and p^2 = {0, 4,6}

We can get {0,4,6} in p^2 or p^3 from {0,2,4,6,8}

So cannot determine.
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09 Aug 2006, 16:13
u2lover wrote:
Given that p is a positive even integer with a positive units digit, if the units digit of p^3 minus the units digit of p^2 is equal to 0, what is the units digit of p + 3?

A 3
B 6
C 7
D 9
E It cannot be determined from the given information.

If units digit = 6 then units(216)-units(36) = 0
p+3 = 9

Hence D

Heman
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09 Aug 2006, 16:20
1
1
haas_mba07 wrote:
Hey U2...
Can you tell me where I missed this question?

My solution is below... goes without saying got it wrong...

haas_mba07 wrote:
E It cannot be determined from the given information.

As p is even,
p = 10x+y

y = {0,2,4,6,8}

Unit's digit of p^3 = {0, 4, 6}
Unit's digit of p^2 = {0,2,4, 6, 8}

As unit's digit p^3 -unit's digit p^2 =0

Common units digit between p^3 and p^2 = {0, 4,6}

We can get {0,4,6} in p^2 or p^3 from {0,2,4,6,8}

So cannot determine.

Since Q says unit digit has to be +ve 0 is out
if 4 is units digit and say # is 4--> 4^3 = 64 & 4^2=16 . Subrtacting units digit does not result in 0.

Try the rest. Only when 6 is in the units digit will 6^3= 216 , 6^2=36. Subtracting units digit will result in zero.

Hence reqd answer = 6+3 = 9 Choice D

Heman
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09 Aug 2006, 16:37
yes... zero is neither positive nor negative so you must leave it alone

I just picked p=2, 4, 6 and got p^3-p^2= 4, 8, 0

p=6 and p+3=9
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11 Aug 2006, 02:50
P is a even number with a positive number in the unit digit
Hence unit digit can be 2,4,6 or 8

2^2 = 4 2^3 = 8
4^2 = 6 4^3 = 4
6^2 = 6 6^3 = 6
8^2 = 4 8^3 = 2

Hence only 6 in the unit digit satisfies the condition given.

hence unit digit of p+3 = 9
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Re: Given that p is a positive even integer with a positive  [#permalink]

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25 Feb 2014, 21:09
Argh, stung again by not reading the question correctly.

Thought it could have been 5 or 6, so picked e.

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Re: Given that p is a positive even integer with a positive  [#permalink]

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04 Mar 2014, 20:32
actionj wrote:
Argh, stung again by not reading the question correctly.

Thought it could have been 5 or 6, so picked e.

As stated above; numbers ending with 0, 1 , 5 , 6 have squares, cubes or any high power returning the same units digit at the end

Example:

5 ^ 10000 would also have 5 at the end
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Given that p is a positive even integer with a positive  [#permalink]

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04 Oct 2015, 23:02
Given: P is an even positive number (i)
and units digit of p^3 - units digit of p^2= 0 (ii)

Required: Units digit of p+3

For (i), The units digit can be 2,4,6 or 8

For (ii), the numbers for which the units digit of cube and square is same are {0, 1, 5, 6}
But we know that p is positive and even.
Hence p = 6

p+3 = 9 Option D
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Re: If positive even integer p has a positive units digit and the units di  [#permalink]

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25 Jan 2017, 00:57
Units digit of cube and square should be equal.
3 units digit satisfy the above condition- 1, 5, 6
p+3 for above units digit are 4,8,9.
Among the options 9 is there.
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Re: If positive even integer p has a positive units digit and the units di  [#permalink]

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25 Jan 2017, 04:04
obliraj wrote:
Units digit of cube and square should be equal.
3 units digit satisfy the above condition- 1, 5, 6
p+3 for above units digit are 4,8,9.
Among the options 9 is there.

I understand that units digits must end in 1 , 5 , and 6 .
Therefore, P + 3 will be 4 , 8 , and 9
But as there are three options , we will not be able to determine a unique answer .
So the answer must be E even though one of the options (that is, 9) is mentioned .
If E would have be any other digit than 4 or 8 then answer would have been D .

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Re: If positive even integer p has a positive units digit and the units di  [#permalink]

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25 Jan 2017, 04:45
1
ziyuenlau wrote:
If positive even integer p has a positive units digit and the units digit of ($$p^{3} – p^{2}$$) is equal to 0, what is the units digit of the quantity $$p + 3$$?

A. 3
B. 6
C. 7
D. 9
E. It cannot be determined from the given information.

Hi sb0541 and obliraj

There is only one possible answer out of 1,5, and 6..
Do not forget the info given.. p is a positive even integer so 6 is the only possibility

$$p^3-p^2$$ has units digit as 0... So p^3 and p^2 should have same digit..
Possible values 1, 5, 0, and 6...
we are looking for POSITIVE even integers
0 and 6 are even and only 6 is positive and even..
So p=6, then p+3=6+3=9

D
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If positive even integer p has a positive units digit and the units di  [#permalink]

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25 Jan 2017, 04:55
ziyuenlau wrote:
If positive even integer p has a positive units digit and the units digit of ($$p^{3} – p^{2}$$) is equal to 0, what is the units digit of the quantity $$p + 3$$?

A. 3
B. 6
C. 7
D. 9
E. It cannot be determined from the given information.

The variable p is a positive even integer and the units digit of this number is also positive. Therefore, the units digit has four possible values: 2, 4, 6, or 8. (O is not a possibility, since 0 is not positive.)

This is useful information because the units digit of a number is the only value that determines the new units digit when that number is squared or cubed. For instance $$1,394^{2} =$$ some very large number whose units digit is 6, because $$4^{2} = 16$$.

In other words, only the units digit of $$p$$ will determine the units digit of $$p^{3}$$ and $$p^{2}$$ . Further, since the units digit of $$p^{3} – p^{2} = 0$$, you’re looking for a circumstance in which the square of the units digit is equal to the cube of the units digit.

When does this occur? Test the possible units digits 2, 4, 6, and 8 to see.

Only when $$p = 6$$ are the units digits of $$p^{3}$$ and $$p^{2}$$ equal—and therefore the units digit of  $$p^{3} – p^{2} = 0$$. As a result, the units digit of p must equal 6, and the units digit of $$p + 3$$ must equal 9.

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