2018 AIME I Problems/Problem 2

The number $n$ can be written in base $14$ as $\underline{a}\text{ }\underline{b}\text{ }\underline{c}$ , can be written in base $15$ as $\underline{a}\text{ }\underline{c}\text{ }\underline{b}$ , and can be written in base $6$ as $\underline{a}\text{ }\underline{c}\text{ }\underline{a}\text{ }\underline{c}\text{ }$ , where $a > 0$ . Find the base- $10$ representation of $n$ .

Solutions

Solution Algebra

We have these equations: $196a+14b+c=225a+15c+b=222a+37c$ . Taking the last two we get $3a+b=22c$ . Because $c \neq 0$ otherwise $a \ngtr 0$ , and $a \leq 5$ , $c=1$ .

Then we know $3a+b=22$ . Taking the first two equations we see that $29a+14=13b$ . Combining the two gives $a=4, b=10$ . Then we see that $222*4+37*1=\boxed{925}$ .

-expiLnCalc

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2018 AIME I Problems/Problem 2

Solutions

Solution Algebra