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# permutations and combinations

the number of arrangements of the word "DELHI" in which E precedes I is

Note by Rama Rao
3 years, 9 months ago

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There are $$5!$$ ways to arrange the letters. Each permutation where E comes before I has a pair where E comes after I (namely swap E and I), so the number of permutations where E comes before I is exactly half of it, or $$5!/2 = 60$$. · 3 years, 9 months ago

If f is a differentiable function and f(x^2-y^2 )=xf(x)-yf(y)  and f(1)=2,then find f(2).

· 3 years, 7 months ago