Three tourists know all three languages, so in the general part of circles we enter number English and 10 people know French, and 3 from them own also German. Therefore, only English and French 10-3=7 people know.
Often in tasks in combination theory sets in which any components repeat meet. For example: in tasks on numbers – figures. For such tasks at placements the formula, and for combinations is used.
Within 30 days of September there were 12 rainy days, 8 windy, 4 cold, 5 rainy and windy, 3 rainy and cold, and one day was both rainy, and windy, and cold. During the how many days in September there was a good weather.
If the X-set, consisting of n of elements, m≤n, placement without repetitions from n of elements of a set of X on m is called the ordered great number of X containing m of elements the ordered great number of X containing m of elements is called.