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If R and S are different integers, both divisible by 5, then which of

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If R and S are different integers, both divisible by 5, then which of [#permalink]

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New post 08 Feb 2018, 08:34
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If R and S are different integers, both divisible by 5, then which of the following is not necessarily true?

(A) R - S is divisible by 5.
(B) RS is divisible by 25.
(C) R + S is divisible by 5.
(B) R^2 + S^2 is divisible by 5.
(E) R + S is divisible by 10.
[Reveal] Spoiler: OA

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If R and S are different integers, both divisible by 5, then which of [#permalink]

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New post 08 Feb 2018, 08:43
Bunuel wrote:
If R and S are different integers, both divisible by 5, then which of the following is not necessarily true?

(A) R - S is divisible by 5.
(B) RS is divisible by 25.
(C) R + S is divisible by 5.
(B) R^2 + S^2 is divisible by 5.
(E) R + S is divisible by 10.


R & S are divisible by 5 so their unit's digit is either 0 or 5

(A) R - S is divisible by 5. ----subtracting the units digit will yield either 0 or 5 hence divisible by 5. True

(B) RS is divisible by 25. -----multiplying will yield either 0 or 5 hence divisible by 5. True

(C) R + S is divisible by 5. -------adding will yield either 0 or 5 hence divisible by 5. True

(B) R^2 + S^2 is divisible by 5. -------as the units digit of both R & S is either 0 or 5, their square will also have unit's digit either 0 or 5. adding the squares will yield either 0 or 5 hence divisible by 5. True

(E) R + S is divisible by 10------will yield either 0 or 5 hence can be divisible by 10, if unit's digit is 0 or cannot be divisible by 10 if unit's digit is 5. Not always true

Option E
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Re: If R and S are different integers, both divisible by 5, then which of [#permalink]

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New post 08 Feb 2018, 08:51
R = 5a; S = 5b

A) R - S = 5(a - b) is divisible by 5

B) RS = 25ab is divisible by 25

C) R + S = 5(a + b) is divisible by 5

D) R^2 + S^2 = 25(a^2 + b^2) is divisible by 5

E) R + S = 5(a + b) is not always divisible by 10

Answer: E
Re: If R and S are different integers, both divisible by 5, then which of   [#permalink] 08 Feb 2018, 08:51
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If R and S are different integers, both divisible by 5, then which of

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