Mean =np Variance =np(1−p) So, np+np(1−p)=1.8 5p+5p(1−p)=1.8 ⇒10p−5p2−1.8=0 ⇒5p2−10p+1.8=0 ⇒5p2−9p−p+1.8=0 ⇒5p(p−1.8)−1(p−1.8)=0 ⇒(p−1.8)(5p−1)=0 ∴p=1.8,0.2 ∵p=1.8 (It is not possible because it is not greater than 1 ) Hence, p=0.2