Seawater weighs 630 grams, has 22 grams of salt, 608 grams of h2o, what % of the seawater is salt?

In chemistry, the mass fraction w_i is the ratio of one substance with mass m_i to the mass of the total mixture m_tot , defined as

w_i = m_i / m_tot.

In your example m_i is the mass of the salt, and m_tot is the mass of the solution. The mass fraction is:

w = 22g / 630g = 0.0349, which is a dimensionless number.

Multiplying mass fraction by 100 gives the mass percentage. It is sometimes called weight percent (wt%) or weight-weight percentage.

wt% = 0.0349 * 100 = 3.49

[Source: en.wikipedia.org/wiki/Mass_fraction_(chemistry) ]