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exercise on selection combination

1. In a school 20 students gave gift to each other, then find the total number of gifts. 2. In how many ways at least 6 players can be selected from a group of 8 players. 3. In how many ways Ramesh can invite 6 friends out of his 15 friends for a dinner. 4. In how...

a work can be compelted by 5 men or 7 women in 4 days. In how many ways labour force can be selected if work has to be finished in 4 days & available labour force is 12 men & 10 women? If labour force has only men or only women

(Q). A work can be compelted by 5 men or 7 women in 4 days. In how many ways labour force can be selected if work has to be finished in 4 days & available labour force is 12 men & 10 women? If labour force has only men or only...

de – arrangement concept

De – arrangement:- Let there are n different colour boxes & correspondingly n different colour balls.Now we are to put these balls into boxes (one in each) such that no two colour matches. = n! – ⁿC₁.(n – 1)! + ⁿC₂.(n – 2)! – ⁿC₃.(n...

inclusion exclusion principle

Inclusion – Exclusion principle:- Number of ways = (Total number of ways) – (number of ways when restriction fails atleast once) + (Number of ways when restriction fails at least twice) – (Number of ways when restriction fails at least thrice) +...