A study was conducted to determine whether flipping a penny or spinning a penny has an effect on the proportion of heads. Among 49,437 trials, 29,015 involved flipping pennies, and 14,709 of those pennies turned up heads. The other 20,422 trials involved spinning pennies, and 9,197 of those pennies turned up heads (based on data from Robin Lock, as given in Chance News).

a. What percentage of the trials involved flipping pennies?
b. What percentage of the trials involved spinning pennies?
c. Among the pennies that were flipped, what is the percentage that turned up heads?
d. Among the pennies that were spun, what is the percentage that turned up heads?