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How many cars are now in the car park?
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One-tenth of the cars in a car park are yellow. Another car arrives and now one-ninth of the cars are yellow.

yellow cars puzzle
How many cars are now in the car park?

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Lets say there are total x cars, thus x/10 number of cars are yellow initially.
As yellow car's percent increases from 1/10th to 1/9th after new car arrives, so new car must be a yellow car.
So we can form the equation as 1 + x/10 = (x+1)/9

Now we just need to solve this equation by multiplying both sides by 9*10
9*10 + 9x = 10x + 10
90 - 10 = 10x - 9x
x = 80

So there were 8 yellow cars initially among a total of 80 cars(i.e. 1/10th)
and a new yellow cars comes making 9 yellow cars in total of 81 cars.(i.e. 1/9th)

So answer to the question is 81. there are a total of 81 cars now.

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