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If n is the sum of the first 40 positive integers, what is the greates
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24 Jun 2021, 09:22
24 Jun 2021, 09:22
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If n is the sum of the first 40 positive integers, what is the greatest prime factor of n?
A. 29
B. 37
C. 41
D. 17
E. 19
A. 29
B. 37
C. 41
D. 17
E. 19
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If n is the sum of the first 40 positive integers, what is the greates
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24 Jun 2021, 09:26
24 Jun 2021, 09:26
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Carcass wrote:
If n is the sum of the first 40 positive integers, what is the greatest prime factor of n?
A. 29
B. 37
C. 41
D. 17
E. 19
A. 29
B. 37
C. 41
D. 17
E. 19
Useful formula: 1 + 2 + 3 + 4 + 5 + . . . .+ k = (k)(k+1)/2
So, for example, 1 + 2 + 3 + 4 + .... + 10 = (10)(10 + 1)/2 = 110/2 = 55
n = 1 + 2 + 3 + 4 + 5 + . . . .+ 40
= (40)(40 + 1)/2
= (40)(41)/2
= (20)(41)
At this point, we can see that 41 will be the greatest prime factor of n.
Answer: C
For "fun" let's finish the prime factorization of n.
We left off at: n = (20)(41)
Continue to get: n = (2)(2)(5)(41)
Cheers,
Brent
gmatclubot
If n is the sum of the first 40 positive integers, what is the greates [#permalink]
24 Jun 2021, 09:26
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