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The product of two positive integers xx and yy is 6760 and their HCF is 13. How many such pairs (x,y)(x, y) can be formed?

Solution

✅ Correct Option: 1

The HCF is 13, so write

x=13ax=13a and y=13by=13b, where aa and bb share no common factor.


xy=6760xy=6760

⇒169ab=6760\Rightarrow 169ab=6760

⇒ab=6760169=40\Rightarrow ab=\dfrac{6760}{169}=40


The coprime factor pairs of 40 are (1,40)(1,40) and (5,8)(5,8). Since (x,y)(x,y) is an ordered pair, their reverses must also be counted.

(a,b)(a,b)(x,y)(x,y)
(1,40)(1,40)(13,520)(13,520)
(40,1)(40,1)(520,13)(520,13)
(5,8)(5,8)(65,104)(65,104)
(8,5)(8,5)(104,65)(104,65)

Therefore, 4 such ordered pairs (x,y)(x,y) can be formed.

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