Question 1 Let a and b be two positive integers such that a = p3q4 and b = p2q3, where p and q are prime numbers. If HCF(a,b) = pmqn and LCM(a,b) = prqs , then (m + n)(r + s) = (a) 15 (b) 30 (c) 35 (d) 72
Given two numbers
a = p3q4 and b = p2q3
Finding HCF
a = p3q4 = p × p × p × q × q × q × q
b = p2q3 = p × p × q × q × q
HCF = p × p × q × q × q
HCF = p2q3
Comparing HCF = p2q3 with HCF = pmqn
∴ m = 2, n = 3
Finding LCM
LCM = p × p × p × q × q × q × q
LCM = p3q4
Comparing LCM = p3q4 with LCM = prqs
∴ r = 3, s = 4
Now,
(m + n)(r + s) = (2 + 3) × (3 + 4)
= 5 × 7
= 35
So, the correct answer is (c)
Made by
Davneet Singh
Davneet Singh is an IIT Kanpur graduate and has been teaching for 16+ years. At Teachoo, he breaks down Maths, Science and Computer Science into simple steps so students understand concepts deeply and score with confidence.
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