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MISCELLANEOUS EXERCISE 8 (II) · Q23

Q.Let X∼B(10,0.2)X\sim B(10, 0.2). Find

(i) P(X=1)P(X = 1)
(ii) P(X≥1)P(X \geq 1)
(iii) P(X≤8)P(X \leq 8).
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✓ Free question

Here n=10n=10, p=0.2p=0.2, q=0.8q=0.8.

  1. P(X=1)=10C1(0.2)1(0.8)9=10×0.2×(0.8)9≈0.2684P(X=1)={}^{10}C_1(0.2)^1(0.8)^9=10\times0.2\times(0.8)^9\approx0.2684.
  2. P(X≥1)=1−P(X=0)=1−(0.8)10≈1−0.1074=0.8926P(X\ge1)=1-P(X=0)=1-(0.8)^{10}\approx1-0.1074=0.8926.
  3. P(X≤8)=1−P(X=9)−P(X=10)P(X\le8)=1-P(X=9)-P(X=10). P(X=9)=10C9(0.2)9(0.8)1≈0.0000041P(X=9)={}^{10}C_9(0.2)^9(0.8)^1\approx0.0000041 and P(X=10)=(0.2)10≈0.0000001P(X=10)=(0.2)^{10}\approx0.0000001, so P(X≤8)≈1−0.0000042=0.9999958P(X\le8)\approx1-0.0000042=0.9999958.
    ✓Final answer

    P(X=1)≈0.2684P(X=1)\approx0.2684; P(X≥1)≈0.8926P(X\ge1)\approx0.8926; P(X≤8)≈0.99999580P(X\le8)\approx0.99999580.

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