A nine-digit number 89563x87y is divisible by 72. What is the value of √7x-3y?
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Correct answer: C
Explanation
The correct answer is option 3 i.e. 6
The number is 89563x87y
If it has to be divisible by 72 i.e. 8 × 9, it has to be divisible by both 8 and 9.
For 89563x87y to be divisible by 8, 87y has to be divisible by 8. Thus, y = 2
For 89563x872 to be divisible by 9 , (8 + 9 + 5 + 6 + 3 + x + 8 + 7 + 2) must be a multiple of 9.
(8 + 9 + 5 + 6 + 3 + x + 8 + 7 + 2) = (48 + x)
If (48 + x) is a multiple of 9, x = 6.
√7x-3y = √7 × 6 - 3 × 2
⇒ √42 - 6 = √36 = 6