What is the prercent by mass of hydrogen in NH3?

The formula shows that there are three times as many atoms of hydrogen as of nitrogen in the compound. The gram atomic masses are 1.00794 for hydrogen and 14.0067 for nitrogen. Therefore, the percent by mass of hydrogen in the compound is 100{[3(1.00794)]/[3(1.00794) + 14.0067] or 17.7553 %, to the justified number of significant digits.