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If x is a positive integer, what is the remainder when 712x+3 + 3 is divided by 5?
  • a)
    0
  • b)
    1
  • c)
    2
  • d)
    3
  • e)
    4
Correct answer is option 'B'. Can you explain this answer?
Verified Answer
If x is a positive integer, what is the remainder when 712x+3 + 3 is d...
To find the remainder when a number is divided by 5, all we need to know is the units digit, since every number that ends in a zero or a five is divisible by 5.
For example, 23457 has a remainder of 2 when divided by 5 since 23455 would be a multiple of 5, and 23457 = 23455 + 2.
Since we know that x is an integer, we can determine the units digit of the number 712x+3 + 3. The first thing to realize is that this expression is based on a power of 7. The units digit of any integer exponent of seven can be predicted since the units digit of base 7 values follows a patterned sequence:
We can see that the pattern repeats itself every 4 integer exponents. 
The question is asking us about the 12x+3 power of 7. We can use our understanding of multiples of four (since the pattern repeats every four) to analyze the 12x+3 power. 
12x is a multiple of 4 since x is an integer, so 712x would end in a 1, just like 74 or 78.
712x+3 would then correspond to 73 or 77 (multiple of 4 plus 3), and would therefore end in a 3.
However, the question asks about 712x+3 + 3.
If 712x+3 ends in a three, 712x+3 + 3 would end in a 3 + 3 = 6.
If a number ends in a 6, there is a remainder of 1 when that number is divided by 5.
The correct answer is B.
 
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Most Upvoted Answer
If x is a positive integer, what is the remainder when 712x+3 + 3 is d...
To find the remainder when 712x^3 - 3 is divided by 5, we need to simplify the expression and then find the remainder.

Simplifying the expression:
712x^3 - 3 can be rewritten as (710x^3 + 2x^3) - 3.

We know that when a number is divided by 5, the remainder can only be between 0 and 4.

To find the remainder of 710x^3 when divided by 5, we can use the concept of modular arithmetic. In modular arithmetic, we take the remainder when a number is divided by another number.

Dividing 710 by 5 gives a remainder of 0. Therefore, the remainder of 710x^3 when divided by 5 is also 0.

To find the remainder of 2x^3 when divided by 5, we can divide each term of 2x^3 by 5 and take the remainder.

2x^3 = (2/5)x^3 * 5 + (2 mod 5)x^3

Since 2 divided by 5 gives a remainder of 2, we can rewrite the expression as:

2x^3 = (2/5)x^3 * 5 + 2x^3

Therefore, the remainder of 2x^3 when divided by 5 is 2x^3.

Now, let's combine the remainders:

(710x^3 + 2x^3) - 3 = (0 + 2x^3) - 3 = 2x^3 - 3.

To find the remainder of 2x^3 - 3 when divided by 5, we can use the same approach as before.

Dividing 2x^3 by 5 gives a remainder of 2x^3.

Dividing -3 by 5 gives a remainder of -3.

Since the remainder has to be between 0 and 4, we can add 5 to the remainder -3 to get a positive remainder:

-3 + 5 = 2.

Therefore, the remainder when 712x^3 - 3 is divided by 5 is 2.

Hence, the correct answer is option B) 2.
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