Integer Properties and Divisibility
GRE · Flashcards · Recall
GRE · FLASHCARDS
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QUESTION
What is the basic divisibility test for
9
9
9
in base
10
10
10
?
QUESTION
What is the basic divisibility test for
6
6
6
in base
10
10
10
?
QUESTION
What is the basic divisibility test for
3
3
3
in base
10
10
10
?
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ANSWER
Divisible by
3
3
3
iff the sum of digits is divisible by
3
3
3
. This rule works because
10
≡
1
(
m
o
d
3
)
10 \equiv 1 \pmod{3}
10
≡
1
(
mod
3
)
, so the number modulo 3 equals the digit sum modulo 3.
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