Every Sunday morning, two children, Craig and Jill, independently try to launch their model airplanes. On each

Question:

Every Sunday morning, two children, Craig and Jill, independently try to launch their model airplanes. On each Sunday, Craig has probability 1/3 of a successful launch, and Jill has probability 1/5 of a successful launch. Determine the expected number of Sundays required until at least one of the two children has a successful launch.