Let the original cost of each puzzle be \( x \).
Since Molly has 6 grandchildren and she buys one puzzle for each, the total cost of the puzzles before the discount is: \[ 6x \]
Given that each puzzle is discounted by 50¢ (or $0.50), the total discounted cost is: \[ 6x - 6(0.50) = 6x - 3 \]
According to the problem, Molly spent a total of $27 on the puzzles, so we can set up the following equation: \[ 6x - 3 = 27 \]
Now, we will solve for \( x \):
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Add 3 to both sides: \[ 6x = 27 + 3 \] \[ 6x = 30 \]
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Divide both sides by 6: \[ x = \frac{30}{6} \] \[ x = 5 \]
Thus, the original cost of each puzzle is: \[ \boxed{5} \]