x - 20/11.13 - 20/13.15 - 20/15.17 - ... - 20/53.55 = 3/11, x - 20/11.13 - 20/13.15 - 20/15.17 -...- 20 53.55 = 3/ 11, x - 20/11 * 13 - 20/13 * 15 - 20/15 * 17 - ... - 20/53 * 55 = 3/11