A two-digit number a b is called almost prime if one obtains a tw… - Vidyadip

MCQ

A two-digit number $\overline{a b}$ is called almost prime if one obtains a two-digit prime number by changing at most one of its digits $a$ and $b$. (For example, $18$ is an almost prime number because $13$ is a prime number). Then the number of almost prime two-digit numbers is

A
$56$
B
$75$
C
$87$
✓
$90$

✓

Answer

Correct option: D.

$90$

d
(d)

Since in the group of first $10$ two digit number $10-19$, has atleast $1$ prime number similarly in other groups of 10 two digits numbers

$20-29$, 30-39, 40-49, 50-59, 60-69, 70-79, $80-89$ and $90-99$ have almost $1$ prime numbers.

So, the number of almost prime two-digit number is $90 .$

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