0.1+0.2x=x

x=1/8=12.5%

Explanation:Let x be the number of ppl exceeding the speed limit

motorists who exceed the posted speed limit do not receive speeding tickets =0.2x

motorists exceed the posted speed limit and receive speeding tickets = 0.1

Therefore, total exceed = Those who exceed and don't recieve ticket + Those who exceed and recieve ticket.

0.1+0.2x=x

It will be easier to visualize if you draw a 2x2 grid with recived tickets/not recieved tickets Vs exceeded/not exceeded.

One needs to be careful dealing with these problems containing statements like these:

1) "but 20% of the motorists who exceed the posted speed limit do not receive speeding tickets" - gives 0.1+0.2x=x => 12.5%

2) "but 20% of the motorists exceed the posted speed limit and they do not receive speeding tickets" - gives 0.1+0.2=0.3 =>30%

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To find what you seek in the road of life, the best proverb of all is that which says:

"Leave no stone unturned."

-Edward Bulwer Lytton