- Home
- Standard 11
- Mathematics
એક વૈકલ્પિક પરીક્ષા $5$ પ્રશ્નો ધરાવે છે. દરેક પ્રશ્ન ત્રણ વૈકલ્પિક જવાબો ધરાવે છે. જે પૈકી એક સાચો હોય છે. તો વિર્ધાર્થીં $4$ અથવા વધારે સાચા જવાબો આપવાની સંભાવના કેટલી ?
$\frac{{17}}{{{3^5}}}$
$\frac{{13}}{{{3^5}}}$
$\frac{{11}}{{{3^5}}}$
$\frac{{10}}{{{3^5}}}$
Solution
Step $- 1$: Simplify the problems to solve using probability
We know that we have 3 alternative answer but only 1 is correct
$\therefore$ The probability of getting a correct answer $\frac{1}{3}$
So the probability of getting an incorrect answer is $\left(1-\frac{1}{3}\right)=\frac{2}{3}$
Step $- 2$: Use binomial distribution
So the probability of getting $4$ or correct answer $=$
probability of $4$ or more correct $+$ probability of $5$ correct answer ………$(i)$
Now we can say, for probability of $4$ correct answer $x=4 \,and\, n=5$
By binomial distribution,Probability of getting $4$ correct answer $=^5 C _4\left(\frac{1}{3}\right)^4\left(\frac{2}{3}\right)^{5-4}$
$=5 \times\left(\frac{1}{3}\right)^4 \times\left(\frac{2}{3}\right)$
$=5 \times \frac{2}{3^5}$
For probability of $5$ correct answer $x=5$ and $n=5$
So the probability of getting $5$ correct answers $={ }^5 C _5 \times\left(\frac{1}{3}\right)^5 \times\left(\frac{2}{3}\right)^{5-5}$
Probability of getting $5$ correct answers $=\left(\frac{1}{3}\right)^5$
Step $- 3:$ Put the values in $(i)$
So the probability of getting $4$ or more correct answers $=5 \times \frac{2}{3^5}+\frac{1}{3^5}$
$=\frac{10}{3^5}+\frac{1}{3^5}$
$=\frac{11}{3^5}$
Hence, the probability that a student will get 4 or more answer correct answer is $\frac{11}{3^5}$