Multiple choice general knowledge math & puzzles

If x and y are the two digits f the number 653xy such that this number is divisible by 80, then x+y is equal to:

  1. 2

  2. 3

  3. 4

  4. 6
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For a number to be divisible by 80, it must be divisible by both 5 and 16. Divisibility by 5 requires the last digit to be 0 or 5. Since xy is a two-digit number at the end, we need 65300 + 100x + 10y ≡ 0 (mod 80). This simplifies to 60 + 10x + y ≡ 0 (mod 80). Testing values, when x=6 and y=0, we get 60 + 60 + 0 = 120, which is divisible by 80. Therefore x+y=6+0=6.

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