Replace 'formula' by 'formulae'. Some nouns have more than one plural form with different meanings.
that govern it.
|Noun (Singular)||Plural I||Meaning||Plural II||Meaning|
|Penny||Pennies||Separate coins||Pence||Collective noun|
|Fish||Fish||Considered collectively||Fishes||Considered separately|
|Shot||Shots||Throw, stroke or hit in certain games||Shots||Firing from the gun|
|Index||Indexe||Tables of contents||Indices||Signs in algebra|
|Cloth||Cloths||Pieces of cloth||Clothes||Garments|
|Brother||Brothers||Sons of the same parent||Brethre||Members of a community or society|