Categories

# Decimal system conversion AMC 10B, 2019 Problem 12

The simplest example of coverting between septal (base 7)and decimal number system. Learn in this self-learning module for math olympiad

## Octal to Decimal system conversion

This problem is based on decimal system conversion. In the given problem we have to convert the given number to the another number system from decimal and finding the sum of the digits later on.

## Try the problem

What is the greatest possible sum of the digits in the base-seven representation of a positive integer less than $2019$?

$\textbf{(A) } 11 \qquad\textbf{(B) } 14 \qquad\textbf{(C) } 22 \qquad\textbf{(D) } 23 \qquad\textbf{(E) } 27$

AMC 10B, 2019 Problem 12

Decimal system conversion

6 out of 10

challenges and thrills of pre college mathematics

## Use some hints

First of all 2019 is in base 10, see below

$2019=2*10^3+0*10^2+1*10^1+9+10^0$.

so we have to convert it in the system having base 7.

After converting we will get

But we have to maximize the sum of digits. So we need to increase the number of 6 in the converted number(in base 7) and it is because 6 is the largest number in the number system having base 7.

The conversion of maximize 6 in the number will occur with either of the numbers $4666_7$ or $5566_7$.

and now we can simply find the sum of the digits.