Final answer:
The specific gravity of SAE 30 oil is approximately 0.919.
Step-by-step explanation:
The specific gravity of a substance is the ratio of its density to the density of water at a specified temperature. It is a measure of the relative density of the substance compared to water.
To find the specific gravity of SAE 30 oil, we need to compare its density to the density of water. The given specific gravity of SAE 30 oil, 57.4 lb/ft3, already provides the necessary information. Since the density of water at 4 degrees Celsius is 62.43 lb/ft3, we can compare the two numbers: 57.4/62.43 = 0.919.
Therefore, the specific gravity of SAE 30 oil is approximately 0.919.