Jambmaths question:
If U ={x: x is an integer and 1≤ x ≤ 20}
E1 = {x: x is a multiple of 3}
E2 = {x: x is a multiple of 4}
and an integer is picked at random from U, find the probability that it is not in E2
Option A:
$\tfrac{3}{4}$
Option B:
$\tfrac{3}{10}$
Option C:
$\tfrac{1}{4}$
Option D:
$\tfrac{1}{20}$
Jamb Maths Solution:
$\begin{align} & U=\{1,2,3,---20\} \\ & n(U)=20,\text{ } \\ & {{E}_{1}}=\{3,6,9,12,15,18\},\text{ }n({{E}_{1}})=6 \\ & {{E}_{2}}=\{4,8,12,16,20\},\text{ }n({{E}_{2}})=5 \\ & E_{2}^{1}=\{1,2,3,5,6,7,9,10,11,13,14,15,17,18,19\} \\ & P({{E}_{2}})=\frac{15}{20}=\frac{3}{4} \\\end{align}$
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