To play the A7 chord, place the index finger on the 1st fret of the C-string. Let the other strings ring open.
A7 Ukulele Chord Explanation
The A7 chord contains the notes A-C#-E-G.
To build an A7 chord, take the dominant seventh formula (1-3-5-b7) and apply it to the A major scale (A, B, C#, D, E, F#, G#).
Identify the first, third, fifth, and flat seventh scale degrees in the A major scale which are A-C#-E-G.
Notice how the seventh scale degree found in the chord is lowered a half step as indicated by the "flat" or "b" that precedes the number "b7". In this case, the seventh scale degree of an A major scale – a "G#" note is lowered a half step to an "G" note to make the chord a dominant seventh chord.
Watch the following video to learn how to play an A7 chord on ukulele.