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Written as products of their prime factors,

N = 2^p x 5^q x 7^r
and
500= 2^2 x 5^3
the hcf of N and 500 is 2^2 x 5^2
the lowest common multiple of N and 500 is 2^3 x 5^3 x 7
find p,q and r

User Poosliver
by
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1 Answer

4 votes

We know that the highest common factor (HCF) of N and 500 is 2^2 x 5^2. So we can write:



N = (2^2 x 5^2) x m (where m is a product of any remaining prime factors in N)



500 = (2^2 x 5^2) x n (where n is a product of any remaining prime factors in 500)



We can simplify these expressions by dividing both sides by 2^2 x 5^2:



N/(2^2 x 5^2) = m


500/(2^2 x 5^2) = n



So, we have:



N/(2^2 x 5^2) = 2^p x 5^q x 7^r/(2^2 x 5^2) = m


500/(2^2 x 5^2) = 2^2 x 5^3/(2^2 x 5^2) = n



Simplifying further:



N/(2^2 x 5^2) = 2^(p-2) x 5^(q-2) x 7^r = m


500/(2^2 x 5^2) = 5 x n



Now, we can compare the prime factors on both sides to find the values of p, q, and r.



Comparing the powers of 2:



For N: p - 2 = 2


=> p = 4



Comparing the powers of 5:



For N: q - 2 = 3


=> q = 5



Comparing the powers of 7:



For N: r = 0 (since there is no 7 in 500)



So we have:



N = 2^4 x 5^5



To find r, we can use the fact that the lowest common multiple (LCM) of N and 500 is 2^3 x 5^3 x 7. Since the LCM is the smallest number that is a multiple of both N and 500, it must contain all the prime factors of N and 500, raised to their highest powers:



LCM = 2^4 x 5^3 x 7^1



Comparing the powers of 7:



For N: r = 1



So we have:



N = 2^4 x 5^5 x 7^0 = 5000



Therefore, p = 4, q = 5, and r = 0, and the prime factorization of N is 2^4 x 5^5 x 7^0 = 5000.

User Maciej Jankowski
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