5‌th monday of April will fall on 29‌th or 30‌th April. again 5‌th thursday of November will fall on 29‌th or 30‌th November. When 29‌th April is Monday. then, Number of days between 29‌th April and 29‌th November = 214 days = 30 weeks + 4 days. thus 29‌th of November would be Friday. But 29‌th November is thursday, hence, 30‌th April is Monday Now, Number of days between 29‌thNovember and 20‌th december = 21 days. = 3 weeks/ Hence, 20‌th december is Thursday