Question
If ${^\text{16}}\text{C}_{\text{r}}={^\text{16}}\text{C}_{\text{r+2}},$ find ${^\text{7}}\text{C}_{4}.$
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$1^2+3^2+5^2+\ldots .+(2 n-1)^2=\frac{n}{3}(2 n-1)(2 n+1)$
(a) From an urn containing 5 gold and 3 silver coins, 3 coins are drawn at random.
(b)5 letters are to be placed into 5 envelopes such that no envelope is empty..
(c)6 books of different subjects are arranged on a shelf.
(d)3 tickets are drawn from a box containing 20 lottery tickets.
(i) {0} (ii) {0, ±1, ±2, ±3}
(iii) $\left\{\frac{1}{2}, \frac{2}{5}, \frac{3}{10}, \frac{4}{17}, \frac{5}{26}, \frac{6}{37}, \frac{7}{50}\right\}$
(iv) {0, -1, 2, -3, 4, -5, 6,…}
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$x_i$
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$10$
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$30$
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$50$
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$70$
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$90$
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$f_i$
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$4$
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$24$
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$28$
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$16$
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$8$
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