Question

54. The unit digit in a two digit number is two
times the digit in tens place. If the digits
are replaced with each other, the number
becomes 18 more than the first number
What is the first number?
(A) 12
(B) 36
(C) 48
(D) 24​

Answer 1

Answer:

c

Step-by-step explanation:

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Answer 2

Subtracting 18 from a number that is two digits ab in decimal such that a=b+2 will always reverse its digits because:

10a+b−18=10(b+2)+b−18=10b+(b+2)=10b+a

Hence you can choose any digits satisfying a=b+2 . For example b=2 gives 42−18=24 .

This works even for non-traditional "digits" such as a=10 (which is 108−18=90 in traditional notation) or b=−1 (which is 9−18=−9 in traditional notation). For example b=42 gives 482−18=464 (forty-two tens plus forty-four ones) ⌣¨