Qian used the rule "divide the length of a piece of wood by 3 to get the number of nails needed. "If 3 nails are needed for a piece of wood that is 9 inches and 13 nails are needed for a piece of wood that is 39 inches, what is the length of a piece of wood that requires 8 nails?
O 18 inches
O 21 inches
O 24 inches
O 27 inches
To solve this problem, we can set up a proportion to find the length of a piece of wood that requires 8 nails.
Let x be the length of the piece of wood.
According to the given information, we have the following proportion:
(9 inches) / 3 nails = (x inches) / 8 nails
Cross-multiplying, we get:
(9 inches) * 8 nails = (x inches) * 3 nails
72 inches = 3x
Dividing both sides by 3, we find:
24 inches = x
Therefore, the length of a piece of wood that requires 8 nails is 24 inches. So the correct answer is option O) 24 inches.