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Let the necessary amount of water be x. Then (1.00)(1 gallon antifreeze) = 0.40(x+1 gallon), or 1 = .40x + .40. Combining like terms: 0.60 = 0.40x.
Then x = 0.60 / 0.40 = 1.5.
Adding 1.5 gallons of water to that 1 gallon of pure antifreeze results in 2.5 gallons of 40% antifreeze.
Answer: Choice A. 4 times
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Explanation:
We'll be using this formula

to compute the average rate of change (AROC) from x = a to x = b. Note how this is effectively the slope formula because y = f(x).
To start things off, we'll compute the AROC from x = 1 to x = 2.

Do the same for the AROC from x = 3 to x = 4.

The jump from m = 10 to m = 40 is "times 4", which is why choice A is the final answer.