Find the mistake in the below maths equations

A = 2
A(A-1) = 2(A-1)
A2-A = 2A-2
A2-2A = A-2
A(A-2) = A-2
A = 1

In the four images below, can you find the odd one out?

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(b) If 20 players took part in the tournament, how many matches were played?