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Hahaha I hope my explanation can make it clearer:

If the ball costs $0.05, that must mean that the bat costs $1.05 (since the bat must cost $1 more than the ball)
Grand Total = $0.05 + $1.05 = $1.10

Most people would say the ball costs $0.10
But if that was the case, the bat must cost $1.10 (since it must cost $1 more than the ball)
Grand Total = $0.10 + $1.10 = $1.20 -> Incorrect

Hope that helps! Whether you understand it or not, you are still awesome, my friend.