2022 AMC 10A Problems/Problem 19
Problem
Define as the least common multiple of all the integers from
to
inclusive. There is a unique integer
such that
What is the remainder when
is divided by
?
Solution
Notice that contains the highest power of every prime below
. Thus,
.
When writing the sum under a common fraction, we multiply the denominators by divided by each denominator. However, since
is a multiple of
, all terms will be a multiple of
until we divide out
, and the only term that will do this is
. Thus, the remainder of all other terms when divided by
will be
, so the problem is essentially asking us what the remainder of
divided by
is. This is equivalent to finding the remainder of
divided by
.
We use modular arithmetic to simplify our answer:
This is congruent to
Evaluating, we get:
Therefore the remainder is
.
~KingRavi
~mathboy282
~Scarletsyc
Solution 2
As in solution 1, we express the LHS as a sum under one common denominator. We note that
Now, we have . We'd like to find
so we can evaluate our expression
Since
don't have a factor of
in their denominators, and since
is a multiple of
multiplying each of those terms and adding them will get a multiple of
, that result is
Thus, we only need to consider
Proceed with solution
to get
.
~sirswagger21
Video Solution By ThePuzzlr
~ MathIsChess
See Also
2022 AMC 10A (Problems • Answer Key • Resources) | ||
Preceded by Problem 18 |
Followed by Problem 20 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | ||
All AMC 10 Problems and Solutions |
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