Basic Specific Gravity question? (Very basic.)?

Question

IF a uniform solid body weighs 50 N in water and 30 N in air, what is it's specific gravity? I know the answer, it is 2.5, but I keep getting 1.67. How do I solve this?

Answer 1

The answer is 1.67 )))

Answer 2

The body weighs 20N less in water than in air. So it displaced 20N of water.

Specific gravity is the ratio of density with respect to water.  We got that the mass of the water is 20 while the mass of the object is 50.  The volume is some value, v, that we don't know. But we do know it is both that of the object and the water it displaced That's key, as you'll see below.

So SG is (50/v)/(20/v). The v cancels, so you get 50/20, or 2.5.