KVPY 2019 SA Exam Previous Papers

A two-digit number $\stackrel{\mathit{–}\mathit{–}\mathit{–}}{\mathit{a}\mathit{b}}$ 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 :