Jery sells children's tickets for half the adult ticket price. if 5 adult tickets and 8 childrens tickets cost a total of $27, what is the cost of an adult ticket?

We can calculate it by listing 2 equations
let x be children ticket price and y be adults
x = y/2. (1)
8x + 5y = 27 (2)
from (1), sub 1 into 2
8 (y/2) + 5y =27
4y + 5y = 27
9y = 27
y = 3
using y = 3 we can go back to (1) and calculate x, but since y is already adult ticket, so we don't necessarily have to.
therefore adult ticket cost $3 each

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.