Question

Calculate the number of integers between $9$ and $99$ having an even tens digit and an odd unit(ones) digit?

• A. $20$
• B. $21$
• C. $19$
• D. $22$

Answer 1

Answer: (A)

$20$

First make a list of even tens digit i.e: $20s,40s,60s$ and $80s$.
Look at $20s$, the number of odd units are $21,23,25,27$ and $29$, then the total are $5$.
Similarly for $40s,60s$ and $80s$

The number of odd units are $5$.
Therefore, the total number of odd units are $4\times 5=20$
Hence, option A is correct.