We will assume that the similar bar that is 3 ft and 3 in long is also made of aluminium, and it only differs from the 4 feet bar by the length.

Let 'x' represent the weight of the 3 ft 3 in long bar.

1 ft = 12 in

1 in = 1/12 ft

3 in = 3/12 ft

3 in = 1/4 ft

3 in = 0.25 ft

3 ft 3 in = 3.25 ft

Since weight = volume x density the weight is directly proportional to the length:

4 : 24 = 3.25 : x

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click here to see the equation solved for x

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x = 19.5 lbs

The weight of the 3 feet 3 inches long aluminium bar is 19.5 pounds.