Correct Answer: C
Explanation:
For how many two-digit positive numbers will tripling the tens digit give us a two digit number that is triple the original number?
Unit digit must be zero
10 ⇒ tripling the ten's digit gives = 30 which is three times of 10 - the original number.
20 ⇒ tripling the ten's digit gives = 60 which is three times of 20 - the original number.
30 ⇒ tripling the ten's digit gives = 90 which is three times of 30 - the original number.
40 ⇒ tripling the ten's digit gives = 120 which is three times of 40 - the original number. But 120 is not of two digit number, so only three numbers meet the given criteria.