Gold density=19.31 if mixed gold density is = 15.47 ? How many % make of gold density 15.47 .......... In other word if density of fools gold is =15.47 ? What is the % of density 15.47

If the density of fool's gold is 15.47 and the density of your sample is 15.47, then your sample is possibly 100% fool's gold and 0% pure gold. (Not likely. See below.)

This source lists the density of fool's gold as being between 4.95 and 5.10. If we suppose it is 5.00 and pure gold has a density of 19.31, we can write an equation for x, the fraction of gold in your sample.
19.51x + 5.00(1-x) = 15.47
19.51x + 5.00 - 5.00x = 15.47    (use the distributive property to eliminate parentheses)
14.52x + 5.00 = 15.47    (collect x terms)
14.52x = 10.47    (subtract 5.00)
x = 10.47/14.52 ≈ .7317    (divide by the x coefficient and evaluate)
Your sample may contain 73% gold.

You will note in the reference above that gold and fool's gold are not usually found together. When they are, the proportion of gold is usually much less than 1%. In order to solve the problem, we needed to know the density of each of the components of the mixture.
thanked the writer. 