Review: Finding Common Ground — Ganita Prakash: Class 7 Mathematics, Part 2 (NCERT)

What You Can Do Now

Tick what you can now do with factors and multiples.

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After this chapter, I can…

HCF or LCM? The Quick Test

How to tell which one a word problem needs.

HCF or LCM?

HCF clues: split into equal parts; the biggest size that fits; the fewest bags or tiles; the longest jump that lands on both.

LCM clues: when do they meet, ring or match again; the shortest length both can make; the smallest number several numbers divide.

Rules: HCF = common primes, fewest times. LCM = all primes, most times. HCF × LCM = product (two numbers only).

Key Terms From This Chapter

Flip through the chapter's key words and rules.

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Questions From the Whole Chapter

Eight questions from quick recall to harder reasoning.

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Prime factorisation of 84?

Step-by-Step Challenge Problems

Three mixed problems with guided steps.

Solve each problem step by step

90 kg and 126 kg of dal are packed in equal bags, each bag from one heap only, using the fewest bags. What weight is each bag, and how many bags are there?
Fewer than 150 mangoes can be shared equally among 4, 6 or 9 children with none left over. How many mangoes could there be? Give every possibility.
Two friends visit a library every 6 and every 8 days. They met there today. When will they next meet there?

HCF or LCM? Why?

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Read the clue words.

Working and answer

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Factorise, compute, answer.

Working and all answers

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Find the LCM, then its multiples under 150.

Working and answer

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HCF or LCM?

Solve It Yourself

Four problems straight from the chapter, no hints.

Solve each problem

Find the HCF of 42, 75 and 24. (Textbook p. 54, Q1b)
Find the LCM of 105, 195 and 65. (Textbook p. 58, c)
Find the HCF and LCM of 630 and 770 with a fast ladder. (Textbook p. 62)
Find two numbers whose HCF is 1 and LCM is 66. (Textbook p. 63, Q4)

HCF of 42, 75, 24

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Show the factorisations.

LCM of 105, 195, 65

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Show the factorisations.

630 and 770

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Show your ladder.

HCF 1, LCM 66

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Check both conditions.

Talk it through: HCF and LCM doubts

Stuck on a factorisation or a word problem? Ask here.

Learners can ask follow-up questions and keep the thread going.

Ask me anything from this chapter: how to tell whether a problem needs the HCF or the LCM, why the HCF takes each prime the fewest times and the LCM the most, why the ladder's bottom row goes into the LCM, or why HCF × LCM = product doesn't work for three numbers. Tell me which question you're on and what you tried. I'll help you find the next step.

almost 3 years ago