CTET Paper II (Mathematics and Science) 21 Dec 2021 Solved Paper

Concept:HCF must always be a factor of LCM. If it is not, the pair is invalid. Explanation:Check each option by dividing LCM by HCF.Option A: HCF=12, LCM=108. 108 ÷ 12 = 9, so 12 is a factor. True.Option B: HCF=25, LCM=180. 180 ÷ 25 = 7.2, not a whole number. False.Option C: HCF=28, LCM=196. 196 ÷ 28 = 7, so 28 is a factor. True.Option D: HCF=15, LCM=210. 210 ÷ 15 = 14, so 15 is a factor. True.Only option B violates the condition. Answer:Option B is not true.