Francaix Divertissement for bassoon and String Quintet?

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5 Usually they are a String Quartet-2 violins, viola and cello; and a piano, although you might see a string quartet and a double Bass.

Five, since a quartet is a form of four, and quintet a form of five. Sextet would be the form for a six instrument piece.

A string quintet has five string instruments, either as 2 violins, 2 violas and one violoncello (as the Mozart string quintets, K. 174, K. 515, K. 516, K. 516b (406), K. 593 & K. 614 or Brahms' 2...

online most likely