Explanation

Starting of menstrual cycle $= 13$ th year of age. Stopping of menstrual cycle = 48 years of age. Duration of menstrual cycle are $= 48 - 13 = 35$ yr Total no. of month is 35 years $= 35 \times 12 = 400$ months One ova is released during one menstrual cycle (one months). So, about 400 ova (follicles) will be produced by a women in its life time