Make formulas that copy correctly

Draft learning material, awaiting human review.

A formula begins with =. Multiplication and division take precedence over addition and subtraction. =10+2*3 gives 16, while =(10+2)*3 gives 36.

A relative reference moves when copied. =B2*C2 filled down one row becomes =B3*C3. Lock a shared rate with dollar signs: =B2*$F$1 keeps the rate in F1 while the row price changes.

$B2 locks the column; B$2 locks the row; $B$2 locks both. To find a proportion, divide a part by a whole. 25/100 is 0.25, displayed as 25%. Check for a zero denominator and use an explicit, meaningful result such as not applicable.

A price is 50 and the tax rate is 8%. The tax is 50*0.08=4; the total is 50*1.08=54.