Pedro and Jon have 20 toy cars altogether if Jon buys another toy car he will have twice as many cars as Pedro how many cars does Pedro?

Let's denote the number of toy cars Pedro has as P and the number Jon has as J. We are given that P + J = 20, and J + 1 = 2P. Substituting the second equation into the first, we get P + (2P - 1) = 20, which simplifies to 3P = 21. Therefore, Pedro has 7 toy cars.