Tens digits

[relaxin99]

What is the tens digit of the positive integer r?

1) The tens digit of r/10 is 3
2) The hundreds digit of 10r is 6

With the answer, can you all please explain how you came up with the answer thanks

[DanaJ]

1. The tens digit of r/10 is actually the hundreds digit of r. Take any example: say you have r = 1230. Notice that 2 is the hundreds digit here. Then divide r by 10 and you get that r/10 = 123. Now, the hundreds digit of r has become the tens digit of r/10. So 1 is insufficient, because it only helps us find the hundreds digit of r and not the tens digit.

2. Using the same line of thought as above, we can conclude that 2 is sufficient. Say r = 367. This means that its tens digit is 6. Multiply r by 10 and you get 10r = 3670, with r's tens digit turning into 10r's hundreds digit. So 6 will be r's tens digit.

Answer B.

[relaxin99]

Again, fantastic explanation....you must be pulling high marks in the Math section of the GMAT