What is the two-digit number? I. Sum of the digits is 7. II. Difference between the number and the number obtained by interchanging the digits is 9. III. Digit in the ten's place is bigger than the digit in the unit's place by 1.
Choose the correct option
A) I and II
B) II and III
C) I and III
D) I and II as well as I and III
E) All
Explanation:   Let the tens and units digit be x and y respectively.   I. x + y = 7.   II. (10x + y) - (10y + x) = 9 x - y = 1.   III. x - y = 1.   Thus, I and II as well as I and III give the answer.   Correct answer is (I and II as well as I and III).
<result>D</result>
What is the two-digit number? I. Sum of the digits is 7. II. Difference between the number and the number obtained by interchanging the digits is 9. III. Digit in the ten's place is bigger than the digit in the unit's place by 1.