A bat and a ball cost $1.10 in total. The bat costs $1.00 more than the ball.
How much does the ball cost?
The ball costs 5c.
Proof
Let the cost of the ball in dollars be \(x\). Then:
\[\begin{align} x + (1+x) & = 1.10 \\ 2 x + 1 & = 1.10 \\ 2 x & = 0.10 \\ x & = 0.05 \\ \end{align}\]Commentry
This is a classic problem because the intuitive answer when hearing the problem is 10c until you stop and calculate it.