The key signature for F major has one flat (B flat) , while the key signature for F minor has four flats (B flat, E flat, A flat, and D flat).
That is the signature for the key of Db. Or, it's relative minor, Bb minor.
When working with flats, the second to last flat is the key signature. The exception here being when only one flat is in the key signature - this would be the key of 'F.' The order of flats are as follows: B-flat, E-flat, A-flat, D-flat, G-flat... etc.
There is no key signature that has Bb and C#.
No key signature has two of the same flat or sharp.
There are three flats in the key signature of E flat major
The key signature of the C minor scale has three flats: B flat, E flat, and A flat.
A key signature
In a key signature, one flat is the note B flat.
The key signature for F major has one flat (B flat) , while the key signature for F minor has four flats (B flat, E flat, A flat, and D flat).
The key signature of the F flat major key has six flats: B flat, E flat, A flat, D flat, G flat, and C flat.
The key signature that has B flat, A flat, E flat and D flat is Concert A flat Major.
Assuming the key signature has only one flat (B Flat) then the key is either F Major, or D minor.
That is the signature for the key of Db. Or, it's relative minor, Bb minor.
To determine the key signature flats in a musical piece, look at the last flat listed in the key signature. This flat indicates the key of the piece. For example, if the key signature has one flat (Bb), the piece is in the key of F major.
One flat in the key signature indicates that the music is in the key of F major or D minor.
When working with flats, the second to last flat is the key signature. The exception here being when only one flat is in the key signature - this would be the key of 'F.' The order of flats are as follows: B-flat, E-flat, A-flat, D-flat, G-flat... etc.