Set 500 to sum of distances traveled by both cars.
This is found using the binomial distribution with P(H) = 1/2 and P(T) = 1/2 n = 15 and r = 10
= nCr(0.5)^(15-10)(0.5)^10
= 15C10 * 0.5^15 = 0.0916 or 9.16%

Hope I helped, also, I used the math thingy, which I haven't used before, so I'm not sure quite how this turned out, well, I guess we will see in a minute! But if it does not work I can try it just typing regularly.
40 minutes to bake a regular sized loaf . . . . tricky question for sure .
An equation for this is 5b. 5 times the number of books (b).