Formula used:
Probability of an event is obtained by dividing the number of favourable outcomes by total number of outcomes.
Complete step-by-step answer:
Given that a letter of English alphabet is chosen at random. We have to find the probability that the chosen letter is a consonant.
Consonants are letters other than vowels in the alphabet.
In English alphabet we have five vowels which are “a, e, i, o & u”.
Since there are $26$ letters in total, we get the number of consonants as $26 - 5 = 21$.
Probability of an event is obtained by dividing the number of favourable outcomes by total number of outcomes.
So here the probability of getting a consonant is found by dividing the number of consonants by the total number of letters in English alphabet.
If $C$ is the event of getting consonant we have,
$P[C] = \dfrac{{21}}{{26}}$
$\therefore $ The probability that the chosen letter is consonant is $\dfrac{{21}}{{26}}$.
Note: We can also solve the problem in another way. We know the sum of probabilities is equal to one. When choosing a letter from English alphabet at random, there are only two possibilities; either vowel or consonant. Since there are five vowels, the probability of getting a vowel is $\dfrac{5}{{26}}$. So the probability of getting consonant is $1 - \dfrac{5}{{26}} = \dfrac{{21}}{{26}}$.