http://french.about.com/library/weekly/aa101300.htm This explains a bit about the different pronunciations. I think in this sentence its up to you whether to pronounce or not!
There are 3 ways of writing 5 + 4 = 9:
- focus on the "=" sign "5 + 4 égal 9"
- focus on "the sum of 5 + 4" = la somme de 5 + 4 égale 9 (verb "égaler", 3rd person singular indicative present)
- focus on the 2 subjects prompting the verb to use the 3rd person plural form: 5 + 4 égalent 9
Mobile glitch is not allowing me to reply to comments, so here is my understanding of the pronounciation of the french "plus" from my 11 years of Canadian french immersion. While plus should be pronounced "plues" people either say the 's' really softly or drop it all together, pronouncing it as "plu" You do have to be aware of the context, because "plue" means rain haha.
"plue" is not part of the conjugation of the verb "pleuvoir". "il a plu" (it rained) is invariable.
"plu" is also the past participle of the verb "plaire": "il m'a plu" (I liked him/it) is invariable as well.
"plus" can be part of a positive or comparative or negative statement, or the sign + :
- j'ai pluS de pommes que toi = I have more apples than you - the S is pronounced
- cinq pluS quatre = five plus four - the S is pronounced
- je n'ai plus de pommes = I no longer have apples - the S is not pronounced.
When "plus" is followed by a word starting with a vowel sound, the S is liaised with the next vowel sound, and it sounds Z
- je n'ai plus Z assez de pommes = I don't have enough apples left
- j'en veux plus Z encore = I want even more of that
[la somme de] cinq plus quatre égale neuf: this is the verb "égaler" in 3rd person singular, present.
cinq plus quatre égal neuf (5+4=9): this is the way we read the signs "+" is "plus" and "=" is "égal"
cinq plus quatre égalent neuf: this is still the verb "égaler" but in 3rd person plural, for a plural subject.