Problem
NT-B1-M10-P007 Unknown Digit and \(11\)
#7
★★☆☆☆ Level 2 of 5
Find the digit \(x\) if \(63x915\) is divisible by \(11\).
Form the alternating sum from the right.
We get \(5-1+9-x+3-6=10-x\). We need \(10-x\equiv0\pmod{11}\). For a digit \(x\), this would require \(x=10\), impossible. Hence no such digit exists.
Important because the answer may be 'none'.