Answer:
So number of cards with 5 written on it = 13
Step-by-step explanation:
On each of the 18 cards, only one number is written: 4 or 5. The sum of the numbers on all the cards is divisible by 17.
Let the number of cards with 5 written on it be x. Then the number of cards with 4 written on it will be (18 - x).
Sum of all numbers is divisible by 17.
Sum of numbers = 5x + 4 (18 - x) = x + 72
The multiple of 17 closest to 72 is 85.
Hence the sum of numbers = 85
x + 72 = 85
x = 13
So number of cards with 5 written on it = 13
