If the 11-digit number 79x6402087y is divisible by 72, then for the smallest value of x, what is the value of (x + 2y)?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 4.
72 = 8 × 9
Divisibility rule of 8: if its last three digits are divisible by 8.
87y ÷ 8,
for: y = 2
872 ÷ 8 = 109
Divisibility rule of 9: A number is divisible by 9 if the sum of its digits is divisible by 9.
Sum of digits = 7 + 9 + x + 6 + 4 + 0 + 2 + 0 + 8 + 7 + 2 = 45 + x
For x = 0, 45 is divisible by 9
⇒ (x + 2y) = 0 + 4 = 4