A B
+ B
____
B A
____
In the correctly worked addition problem above, A and B represent digits. What is A?
(A) 5
(B) 6
(C) 7
(D) 8
(E) 9
A and B represent digits
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Answer is 8
10A +B +B = 10B +A
a/b =8/9
10A +B +B = 10B +A
a/b =8/9
Its do or die this time!
Practise, practise and practise.
Practise, practise and practise.
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Alternatively, we can apply some logic here.sanju09 wrote:A B
+ B
____
B A
____
In the correctly worked addition problem above, A and B represent digits. What is A?
(A) 5
(B) 6
(C) 7
(D) 8
(E) 9
We can make 2 conclusions:
1) When we add B+B the units digit of the sum is A
This means that A must be even. So, we can eliminate A, C and E.
2) When we add B+B, the sum is greater than 9.
We know this because we begin with a tens digit of A (as in AB) and once we add B, the sum becomes BA where the tens digit is now B.
Since we already know that the answer is B or D, we can just check each one.
This won't take long since we need only check one of these answer choices. If B works, we're done. If B doesn't work, the answer must be D.
Let's check answer choice B, which says A=6
If A = 6, then B must equal 8 (since 8+8=16)
If A=6 and B=8, we get: 68+8=86 (doesn't work, eliminate B)
So, the answer must be D
. . . Now, if we want to kill some time before the next question we could check this answer choice, but I'd just move on to the next question.
Let's check answer choice D (for the timid )
Answer choice D says A=8
If A = 8, then B must equal 9 (since 9+9=18)
If A=8 and B=9, we get: 89+9=98 (WORKS!)
So, the answer is D
Cheers,
Brent
For some reason, this question is very confusing to me.
How did you come up with your first statement that "When we add B+B the units digit of the sum is A
This means that A must be even. So, we can eliminate A, C and E."
I'm lost. Thanks!
How did you come up with your first statement that "When we add B+B the units digit of the sum is A
This means that A must be even. So, we can eliminate A, C and E."
I'm lost. Thanks!
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Let's examine some sums of two numbers that have the same units digit.deojason wrote: How did you come up with your first statement that "When we add B+B the units digit of the sum is A
This means that A must be even. So, we can eliminate A, C and E."
23 + 3 = 26
51 + 1 = 52
87 + 7 = 94
14 + 4 = 18
Notice that the units digit of the sum is equal to the units digit in the sum of two identical units digits.
Cheers,
Brent
Awesome! Thanks a lot! That makes sense now. I feel funny I didn't catch it the first time. I think it's time to rest since I've been watching your videos on Youtube, reading blogs, and answering practice questions for at least 5 hours now. LOL
Thanks a lot! You're a great help!
Thanks a lot! You're a great help!
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We can apply some logic here.sanju09 wrote:A B
+ B
____
B A
____
In the correctly worked addition problem above, A and B represent digits. What is A?
(A) 5
(B) 6
(C) 7
(D) 8
(E) 9
We can make 2 conclusions:
1) When we add B+B the units digit of the sum is A
This means that A must be even. So, we can eliminate A, C and E.
2) When we add B+B, the sum is greater than 9.
We know this because we begin with a tens digit of A (as in AB) and once we add B, the sum becomes BA where the tens digit is now B.
Since we already know that the answer is B or D, we can just check each one.
This won't take long since we need only check one of these answer choices. If B works, we're done. If B doesn't work, the answer must be D.
Let's check answer choice B, which says A=6
If A = 6, then B must equal 8 (since 8+8=16)
If A=6 and B=8, we get: 68+8=86 (doesn't work, eliminate B)
So, the answer must be D
. . . Now, if we want to kill some time before the next question we COULD check this answer choice, but I'd just move on to the next question.
Let's check answer choice D (for the timid! )
Answer choice D says A=8
If A = 8, then B must equal 9 (since 9+9=18)
If A=8 and B=9, we get: 89+9=98 (WORKS!)
So, the answer is D
Cheers,
Brent
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As written AB + B = BA representing digits.sanju09 wrote:A B
+ B
____
B A
____
In the correctly worked addition problem above, A and B represent digits. What is A?
(A) 5
(B) 6
(C) 7
(D) 8
(E) 9
https://www.crushthetest.com
So 10A + 2B = 10B + A
Rearranging, 9A - 8B = 0
So 9A= 8B. Pretty easy to see the LCM is 72
therefore A=8, D and B = 9
Hi Brent,Brent@GMATPrepNow wrote:Alternatively, we can apply some logic here.sanju09 wrote:A B
+ B
____
B A
____
In the correctly worked addition problem above, A and B represent digits. What is A?
(A) 5
(B) 6
(C) 7
(D) 8
(E) 9
We can make 2 conclusions:
1) When we add B+B the units digit of the sum is A
This means that A must be even. So, we can eliminate A, C and E.
2) When we add B+B, the sum is greater than 9.
We know this because we begin with a tens digit of A (as in AB) and once we add B, the sum becomes BA where the tens digit is now B.
Since we already know that the answer is B or D, we can just check each one.
This won't take long since we need only check one of these answer choices. If B works, we're done. If B doesn't work, the answer must be D.
Let's check answer choice B, which says A=6
If A = 6, then B must equal 8 (since 8+8=16)
If A=6 and B=8, we get: 68+8=86 (doesn't work, eliminate B)
So, the answer must be D
. . . Now, if we want to kill some time before the next question we could check this answer choice, but I'd just move on to the next question.
Let's check answer choice D (for the timid )
Answer choice D says A=8
If A = 8, then B must equal 9 (since 9+9=18)
If A=8 and B=9, we get: 89+9=98 (WORKS!)
So, the answer is D
Cheers,
Brent
I think there is a typo in the analysis of the answer B. 68+8= 76 (not 86) making it unsuitable for the answer.
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I'm not saying that 68+8=86Shamanthi wrote:Hi Brent,Brent@GMATPrepNow wrote:Alternatively, we can apply some logic here.sanju09 wrote:A B
+ B
____
B A
____
In the correctly worked addition problem above, A and B represent digits. What is A?
(A) 5
(B) 6
(C) 7
(D) 8
(E) 9
We can make 2 conclusions:
1) When we add B+B the units digit of the sum is A
This means that A must be even. So, we can eliminate A, C and E.
2) When we add B+B, the sum is greater than 9.
We know this because we begin with a tens digit of A (as in AB) and once we add B, the sum becomes BA where the tens digit is now B.
Since we already know that the answer is B or D, we can just check each one.
This won't take long since we need only check one of these answer choices. If B works, we're done. If B doesn't work, the answer must be D.
Let's check answer choice B, which says A=6
If A = 6, then B must equal 8 (since 8+8=16)
If A=6 and B=8, we get: 68+8=86 (doesn't work, eliminate B)
So, the answer must be D
. . . Now, if we want to kill some time before the next question we could check this answer choice, but I'd just move on to the next question.
Let's check answer choice D (for the timid )
Answer choice D says A=8
If A = 8, then B must equal 9 (since 9+9=18)
If A=8 and B=9, we get: 89+9=98 (WORKS!)
So, the answer is D
Cheers,
Brent
I think there is a typo in the analysis of the answer B. 68+8= 76 (not 86) making it unsuitable for the answer.
I'm saying that, if A=6 and B=8, then our equation (AB + B = BA) becomes 68 + 8 = 86
Since this equation is faulty, we can eliminate answer choice B
Cheers,
Brent