It is. It's considered both string and percussion because of the
mallets that strike the inside of the piano to make sound
(percussion), and the strings inside of the piano (strings).
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The piano is a percussion instrument because it has hammers
inside it which strike the strings. A percussion instrument is one
where something is hit to make a sound.
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The piano is a percussion instrument because it has hammers
inside it which strike the strings. A percussion instrument is one
where something is hit to make a sound.