Multiplication the same as addition

Multiplication never gives the same result as addition. Or does it?

If a a , b b , and c c are non-negative integers, b b and c c are relatively prime, and a + b c = a × b c a+\frac{b}{c}=a\times\frac{b}{c} , then what is b c b-c ?


The answer is 1.

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3 solutions

Andy Hayes
Nov 17, 2015

Let y = b c y=\frac{b}{c} . Then a + y = a y a+y=ay . Solving this equation for y y yields y = a a 1 y=\frac{a}{a-1} . Thus, b = a b=a , c = a 1 c=a-1 , and b c = 1 b-c=\boxed{1} .

What does relatively prime mean?

Debmeet Banerjee - 5 years, 6 months ago

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Relatively prime means that the integers have no common factors other than 1. Saying that the numerator and denominator of a fraction are 'relatively prime' is another way of saying that the fraction is in reduced terms.

Andy Hayes - 5 years, 6 months ago

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Oh, that means relatively prime is equivalent to co prime.

Debmeet Banerjee - 5 years, 6 months ago

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@Debmeet Banerjee Yes! They are equivalent.

Andy Hayes - 5 years, 6 months ago
Saptarshi Sen
Dec 4, 2015

x+y=xy is possible only if x and y are equal to 2 ................i know it's pure logic

A couple examples:

3 + 3 2 = 3 × 3 2 = 9 2 3+\frac{3}{2}=3\times\frac{3}{2}=\frac{9}{2}

7 + 7 6 = 7 × 7 6 = 49 6 7+\frac{7}{6}=7\times\frac{7}{6}=\frac{49}{6}

Andy Hayes - 5 years, 6 months ago
Guido Barta
Dec 1, 2015

a + b/c= a*b/c means that a+b/c= b/c+b/c+....+b/c ( a times). just bring one b/c from the right side to the left side and you have : a=(a-1)b/c, now divide both side for ( a-1) and you obtain b=a,c=a-1 so a-(a-1) is equal to 1...my first solution on brilliant..hope you like it

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