Question 151039
Let the code be ABCDE.
1.{{{E+C=14}}}
2.{{{D=B+1}}}
3.{{{A=2B-1}}}
4.{{{B+C=10}}}
5.{{{A+B+C+D+E=30}}}
Let's see if we can get each number in terms of B.
From 3,
{{{A=2B-1}}}
From 4,
{{{B+C=10}}}
{{{C=10-B}}}
From 2,
{{{D=B+1}}}
From 1 and 4,
{{{E+C=14}}}
{{{E=14-C}}}
{{{E=14-(10-B)}}}
{{{E=14-10+B}}}
{{{E=B+4}}}
Now substitute all of these into 5 and solve for B.
5.{{{A+B+C+D+E=30}}}
{{{(2B-1)+B+(10-B)+(B+1)+(B+4)=30}}}
{{{B(2+1-1+1+1)+(-1+10+1+4)=30}}}
{{{4B+14=30}}}
{{{4B=16}}}
{{{B=4}}}
Now go back and find A,C,D,and E.
{{{A=2B-1=2(4)-1=8-1=7}}}
{{{C=10-B=10-4=6}}}
{{{D=B+1=4+1=5}}}
{{{E=B+4=4+4=8}}}
His number was 74658. 
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The question to ask is how could he remember these find intricate codes but not 5 numbers.