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Re: How many positive integers less than 1000 are 6 times the sum of their [#permalink]
can u explain why x was equated to zero

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Re: How many positive integers less than 1000 are 6 times the sum of their [#permalink]
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Aderonke01 wrote:
can u explain why x was equated to zero

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please see gmatprepnow solution above..
quoting below:

IMPORTANT: Since x, y and z are DIGITS (from 0 to 9), we can see that x must equal zero
IF, for example, if x has a non-zero value like x = 1, we get: 94 + 4y = 5z, and there are no DIGIT values of y and z that can satisfy the equation.
So, x must be zero.
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Re: How many positive integers less than 1000 are 6 times the sum of their [#permalink]
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Bunuel wrote:
How many positive integers less than 1000 are 6 times the sum of their digits?

(A) 0
(B) 1
(C) 2
(D) 4
(E) 12


We can see that the integers, if they exist, are either 2 digits or 3 digits since there is no 1-digit number that is 6 times itself. If the number is 2 digits, we can create the equation:

10a + b = 6(a + b)

10a + b =6a + 6b

4a = 5b

We see that a = 5 and b = 4. If other words, the number 54 is 6 times of the sum of its digits. Notice that 6(5 + 4) = 6(9) = 54.

If the number is 3 digits, we see that the hundreds digit has to be 1. If the hundreds digit is 2 or more, we see that the quotient between the number and 6 is more than 30, but the sum of its digits is no more than 3 x 9 = 27. So we can create the equation:

100 + 10c + d = 6(1 + c + d)

100 + 10c + d = 6 + 6c + 6d

94 + 4c = 5d

We see that there is no solution for the above equation since the right hand side is at most 45 but the left hand side is at least 94.

Therefore, 54 is the only integer that is less than 1000 which is 6 times the sum of its digits.

Answer: B
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Re: How many positive integers less than 1000 are 6 times the sum of their [#permalink]
ScottTargetTestPrep wrote:
Bunuel wrote:
How many positive integers less than 1000 are 6 times the sum of their digits?

(A) 0
(B) 1
(C) 2
(D) 4
(E) 12


We can see that the integers, if they exist, are either 2 digits or 3 digits since there is no 1-digit number that is 6 times itself. If the number is 2 digits, we can create the equation:

10a + b = 6(a + b)

10a + b =6a + 6b

4a = 5b

We see that a = 5 and b = 4. If other words, the number 54 is 6 times of the sum of its digits. Notice that 6(5 + 4) = 6(9) = 54.

If the number is 3 digits, we see that the hundreds digit has to be 1. If the hundreds digit is 2 or more, we see that the quotient between the number and 6 is more than 30, but the sum of its digits is no more than 3 x 9 = 27. So we can create the equation:

100 + 10c + d = 6(1 + c + d)

100 + 10c + d = 6 + 6c + 6d

94 + 4c = 5d

We see that there is no solution for the above equation since the right hand side is at most 45 but the left hand side is at least 94.

Therefore, 54 is the only integer that is less than 1000 which is 6 times the sum of its digits.

Answer: B


Can you please explain this line - with an example if possible?

If the number is 3 digits, we see that the hundreds digit has to be 1. If the hundreds digit is 2 or more, we see that the quotient between the number and 6 is more than 30, but the sum of its digits is no more than 3 x 9 = 27. So we can create the equation:
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Re: How many positive integers less than 1000 are 6 times the sum of their [#permalink]
Expert Reply
Mansoor50 wrote:
ScottTargetTestPrep wrote:
Bunuel wrote:
How many positive integers less than 1000 are 6 times the sum of their digits?

(A) 0
(B) 1
(C) 2
(D) 4
(E) 12


We can see that the integers, if they exist, are either 2 digits or 3 digits since there is no 1-digit number that is 6 times itself. If the number is 2 digits, we can create the equation:

10a + b = 6(a + b)

10a + b =6a + 6b

4a = 5b

We see that a = 5 and b = 4. If other words, the number 54 is 6 times of the sum of its digits. Notice that 6(5 + 4) = 6(9) = 54.

If the number is 3 digits, we see that the hundreds digit has to be 1. If the hundreds digit is 2 or more, we see that the quotient between the number and 6 is more than 30, but the sum of its digits is no more than 3 x 9 = 27. So we can create the equation:

100 + 10c + d = 6(1 + c + d)

100 + 10c + d = 6 + 6c + 6d

94 + 4c = 5d

We see that there is no solution for the above equation since the right hand side is at most 45 but the left hand side is at least 94.

Therefore, 54 is the only integer that is less than 1000 which is 6 times the sum of its digits.

Answer: B


Can you please explain this line - with an example if possible?

If the number is 3 digits, we see that the hundreds digit has to be 1. If the hundreds digit is 2 or more, we see that the quotient between the number and 6 is more than 30, but the sum of its digits is no more than 3 x 9 = 27. So we can create the equation:



For a three-digit integer, the maximum value for the sum of the digits is 27 (which is the sum of the digits of the three-digit number 999). Thus, for any three-digit integer, the maximum value of 6 times the sum of the digits is 6 x 27 = 162. Even the smallest possible three-digit integer with a hundreds digit of 2 (which is 200) exceeds 162; that’s why, if 6 times the sum of the digits is to equal the number, the hundreds digit must be 1.
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Re: How many positive integers less than 1000 are 6 times the sum of their [#permalink]
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Re: How many positive integers less than 1000 are 6 times the sum of their [#permalink]
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