Here, `n = 4`, `p = 0.8`, `q = 0.2`.

Let `X =` number of hits.

Let x0 = no hits, x1 `= 1` hit, x2 `= 2` hits, etc.

(a) `P(X)=P(x_3)+P(x_4)`

`=C_3^4(0.8)^3(0.2)^1+` `C_4^4(0.8)^4(0.2)^0`

`=4(0.8)^3(0.2)+(0.8)^4`

`=0.8192`

(b) `3` misses means `1` hit, and `4` misses means `0` hits.

`P(X)=P(x_1)+P(x_0)`

`=C_1^4(0.8)^1(0.2)^3+` `C_0^4(0.8)^0(0.2)^4`

`=4(0.8)^1(0.2)^3+(0.2)^4`

`=0.0272`

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