Taking your 99% effectiveness of the pill, the probability of the failure of that is 1%, or 0.01. The probability of failure of the pull-out method (done correctly) is 4%, or 0.04. Combining the two, means the probability of simultaneous failure is 0.01*0.04 = 0.0004, or 0.04%, or 1 out of 2500 times.
This is in the form of retinal activity equivalents to account for the various sources of vitamin A. The best sources of preformed vitamin A are in liver and fish oils. This includes beef, calf, chicken liver and cod liver oil.
Green leafy vegetables and orange vegetables and fruits supply vitamin A in the form of carotenoids. To easily meet your recommended intakes, the Dietary Guidelines for Americans suggests 3 cups per week of dark leafy green vegetables and 2 cups per week of orange vegetables.hat are the best food sources? Preformed vitamin A (a.k.a. retinol) is found in foods of animal origin, such as liver, eggs, milk fortified with vitamin A, fortified cereals and fish.