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CEMC Gauss (Grade 8), 2024

Number theory Difficulty 1.4 Junior Find the answer Canada

The number $385$ has three
prime factors. The sum of these prime factors is

Pick one

Solutions — 2

Solution 1

Since $385$ has a units digit
of $5$ , then it is divisible by $5$ . Dividing, we get $\frac{385}{5}=77$ .

Since $77=7\times11$ , then the three
prime factors of $385$ are $5$ , $7$
and $11$ , and their sum is $5+7+11=23$ .

Solution 2

Since 385 has a units digit of $5$ , then it is divisible by $5$ . Dividing, we get $\frac{385}{5}=77$ .

Since $77=7\times11$ , then the three
prime factors of $385$ are $5$ , $7$
and $11$ , and their sum is $5+7+11=23$ .

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