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.
Tens digits
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Source: Beat The GMAT — Data Sufficiency |
