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Re: A, B and C are different prime numbers, and positive integer D is a no [#permalink]
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firas92 wrote:
chetan2u wrote:
GMATPrepNow wrote:
A, B and C are different prime numbers, and positive integer D is a non-prime number. If D divided by C equals B with remainder A, what is the smallest possible value of B + C?

A) 8
B) 10
C) 12
D) 14
E) 18



You can have umpteen values for A, B , C and D..
Now, \(D=B*C+A\)
One restriction is that A has to be the smallest, so let it be 2, then B and C can be 3 and 5.
Thus \(D=3*5+2=17\), but 17 is prime so D turns out to be prime.
Similarly, when B and C are 3 and 7, \(D=3*7+2=23\), but 23 is prime so D turns out to be prime.

Next possibility is when A=3, and B and C can be checked for other values.
But our answers are even, so B and C both must be even..
Also in every case BC+A or D will be EVEN when A, B and C are ODD.
Hence B and C can take next larger values after A or 3, so B and C are 5 and 7, and 5+7=12..


C


chetan2u

How about A=5, B=3, C=7, D=26? A just has to be smaller than C

26=3*7+5

In which case B+C=10


HI
you are correct. I did check for A as 3 and B as 2 with C as 5 and 7, but missed out checking for A=5.
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Re: A, B and C are different prime numbers, and positive integer D is a no [#permalink]
1
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We know that

D= B * C + A
A<C

take B=3; C=5 and A=3
--> 18 = 3 * 5 + 3 --> min(B +C) = 8

All restrictions are satisfied, is there anything wrong in my reasoning?
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Re: A, B and C are different prime numbers, and positive integer D is a no [#permalink]
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Top Contributor
Camach700 wrote:
We know that

D= B * C + A
A<C

take B=3; C=5 and A=3
--> 18 = 3 * 5 + 3 --> min(B +C) = 8

All restrictions are satisfied, is there anything wrong in my reasoning?


Good idea!
The problem is that the question says "A, B and C are different prime numbers"
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Re: A, B and C are different prime numbers, and positive integer D is a no [#permalink]
Why cant A be 7 when I take B as 3 and C as 5?
15 + 7 gives me 22 which is not prime

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Re: A, B and C are different prime numbers, and positive integer D is a no [#permalink]
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ashdank94 wrote:
Why cant A be 7 when I take B as 3 and C as 5?
15 + 7 gives me 22 which is not prime

Posted from my mobile device


A has to be less than C.

D divide by C or 5 cannot give A or 7 as remainder. Remainder has to be less than the divisor or 5 here.
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Re: A, B and C are different prime numbers, and positive integer D is a no [#permalink]
Given: A, B and C are different prime numbers, and positive integer D is a non-prime number.
Asked: If D divided by C equals B with remainder A, what is the smallest possible value of B + C?

D = BC + A

Prime numbers = {2,3,5,7,11,13,17,19,23,29,}

For the smallest possible value of B+C, BC = 2*3 = 6; B+C=5; No value of A is possible; Rejected
For next smallest possible value of B+C, BC = 2*5 = 10; B+C=7; A=3; D= 13; Rejected
For next smallest possible value of B+C, BC = 3*5 = 15; B+C=8; A=2; D=17; Prime; Rejected
For next smallest possible value of B+C, BC = 2*7 = 14; B+C=9; A=3; D=17; Prime; Rejected; A=5;D=19;Prime; Rejected
For next smallest possible value of B+C, BC = 3*7 = 21; B+C=10; A=2; D=23; Prime; Rejected; A=5;D=26=2*13; Non-prime: Accepted

26 = 3*7 + 5
D = 26; C=7; B=3; A=5; B+C = 3+7 = 10

​​​​​​​IMO B­
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Re: A, B and C are different prime numbers, and positive integer D is a no [#permalink]
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