Ed is doing a survey of popular colors for cars for a school report. he decides to take a sample by sitting near a busy intersection and noting the colors of the cars as they go by him. ed counts 23 black cars, 9 red cars, 17 blue cars, 25 white cars, and 21 silver cars during 20 minutes of watching. how many more white and blue cars are there than silver and red cars?

The answer is 12.

If we represent the cars in this way:
Black cars  A = 23
Red cars    B = 9
Blue cars   C = 17
White cars D = 25
Silver cars E = 21

Then sum of white and blue cars is D + C = 25 + 17 = 42
And the sum of silver and red cars is E + B = 21 + 9 = 30

Using the subtraction:
(D+C) - (E+B) = 42 - 30 = 12

Therefore, there are 12 more white and blue cars than silver and red cars.