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Which pair of numbers is relatively prime?

A. 112 and 36
B. 275 and 77
C. 625 and 81
D. 800 and 95

User Ofek
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2 Answers

7 votes

Answer:

The answer is C

Explanation:

To find which pair of numbers is relatively prime, start by finding all the factors for each pair of numbers. The numbers one hundred twelve and thirty-six are both even numbers, so two is a factor of them both. Therefore, one hundred twelve and thirty-six are not relatively prime. The factors of two hundred seventy-five are one, five, eleven, twenty-five, fifty-five, and two hundred seventy-five. The factors of seventy-seven are one, seven, eleven, and seventy-seven. They share eleven as a common factor, which means that two hundred seventy-five and seventy-seven are not relatively prime. The factors of six hundred twenty-five are one, five, twenty-five, one hundred twenty-five, and six hundred twenty-five. The factors of eighty-one are one, three, nine, twenty-seven, and eighty-one. The only factor common to both numbers is one. So, six hundred twenty-five and eighty-one are relatively prime. The numbers eight hundred and ninety-five each have a common factor of five, as well as one. So, these two numbers are not relatively prime. The pair of numbers that are relatively prime is six hundred twenty-five and eighty-one.

User Shimon
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5.3k points
4 votes

Answer: C. 625 and 81

Step-by-step explanation: A relatively prime pair is a pair in which in both numbers given, the only number that can go into each number is one. In 112 and 36, we know 2 can evenly go into each number because they both end in a positive number (112/2 is 56 and 36/2 is 18.) This means A is incorrect. As for B, 11 can evenly go into each number, leaving you with 25 and 7. B is incorrect. And then there's D. 5 can go into each number giving you 160 and 19. D is incorrect.

C is correct because the only numbers that can go evenly into 81 is 1, 3, 9, 27, and 81. None of these numbers, except one can go into 625 also.

User Aleister
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4.9k points