<prompt> In calendar method of contraception, first day of feile period is?10th day of shoest menstural cycle18th day of shoest menstural cycle10th day of longest menstural cycle18th day of longest menstural cycle  <response>: Ans. is a i.e. 10th day of shoest menstural cycle o Shoest period gives information about the first day of the feile period. The shoest cycle minus 18 days gives first day of feile period. For example, in a cylce of 28 days most common, first day of feile period will be 10th day of cycle 28 -18 10. o Longest period gives information about the last day of the feile period. The longest cycle minus 10 days gives the last day of feile period. For example, in a cycle of 28 days, last day of feile period will be 18th day of cycle 28 - 10 18. 