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.
This chart will help you find foods that are a good source of vitamin A. Both animal and plant foods have vitamin A activity. Retinol, also called preformed vitamin A, is the natural form found in animals.Carotenoids, found in plants, are compounds that the body can convert to vitamin A.Liver is the single best food source of vitamin A. However, many experts recommend eating liver only once or twice a month because of the toxic substances it can contain. Environmental pollutants tend to congregate in an animal's liver.oth animal and plant foods have vitamin A activity. Retinol, also called preformed vitamin A, is the natural form found in animals. Carotenoids, found in plants, are compounds that the body can convert to vitamin A.