Step 1: Analyse Question StemIn questions involving Numbers and Digits, like this one here, it is good practice to think of the Place value concept.
Many test takers would write A = xy and B = yx; however, if you would like to create expressions / equations, you need to practice writing A = 10x + y and B = 10y + x, which are the numbers expressed in terms of the respective place values of their digits.
We also know that Q = 10B – A. Substituting the values of B and A, we have,
Q = 10 (10y + x) – (10X +y)
= 100y + 10x – 10x – y
= 99y
Therefore, to find the value of Q, we need the value of y, which is the units digit of the number A and also the tens digit of number B.
Step 2: Analyse Statements Independently (And eliminate options) – AD / BCEStatement 1: The tens digit of A is 7.
This means that x = 7. We have no data about y.
Statement 1 alone is insufficient, answer options A and D can be eliminated.
Statement 2: The tens digit of B is 6.
This means that y = 6. This is sufficient to find out the value of Q, as per our analysis of the question.
Statement 2 alone is sufficient, answer options C and E can be eliminated.
The correct answer option is B. _________________
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