To find the original cost of each puzzle, we first determine how much Molly spent on each puzzle after the discount.
Let \( x \) be the original cost of each puzzle. Since the puzzles are discounted by $0.50, the cost of each puzzle after the discount is:
\[ x - 0.50 \]
Molly has 6 grandchildren, so she buys 6 puzzles. The total amount she spent on the puzzles is $27. Therefore, we can set up the equation:
\[ 6(x - 0.50) = 27 \]
Next, we can distribute the 6:
\[ 6x - 3 = 27 \]
Now, we add 3 to both sides of the equation:
\[ 6x = 30 \]
Next, we divide both sides by 6 to solve for \( x \):
\[ x = 5 \]
Thus, the original cost of each puzzle is:
\[ \boxed{5} \text{ dollars.} \]
To verify, if the original price is $5, then the discounted price is:
\[ 5 - 0.50 = 4.50 \]
If Molly buys 6 puzzles at the discounted price:
\[ 6 \times 4.50 = 27 \]
This confirms that the calculations are correct. Therefore, the original cost of each puzzle is indeed \( \boxed{5} \) dollars.