Determine the number of moles in a 15.4 gram sample of zinc

Steps to solve:
1. Look at periodic table and locate zinc and its mass number. 

Zn has a mass of 68.38 g/mol (grams per mole)

2. The mass number will help us convert grams into moles, because it gives us the conversion rate.

We have 15.4 grams of Zn. 
We know that in one mole of Zn, there is 68.38 moles. 

3. Convert grams to moles by multiplying 15.4 by 1/68.38. 

15.4 grams of Zn x  = 0.225 moles Zn

The general equation for converting is 

number in starting unit x  = wanted units

While unproven, it uses facts to support part of a conclusion. it is still factual and has predictive power, however.