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.
Vitamin A, a fat-soluble vitamin, plays an important role in bone growth, reproduction, immune function, hormone synthesis and regulation, and vision. Your eyes need vitamin A to help them convert light into brain signals that allow you to perceive images.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.