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Coin riddles
Joyful Mathematics: Chapter 13
GoalFind coins that make an amount by trying and checking.
New words
try · test an ideacheck · add to see if it is righthidden · covered, not shown
Explanation
A coin riddle tells how many coins and how much money. I have 2 coins that make ₹7. Try ₹5 and ₹2, then add: 5 + 2 = 7. It is right. If not, try other coins.
Worked examples
3 coins make ₹9. They are ₹5, ₹2 and ₹2.
2 coins make ₹15. They are ₹10 and ₹5.
2 coins make ₹4. They are ₹2 and ₹2.
Class activity
Coin riddles at home. Make paper coins of ₹1, ₹2, ₹5 and ₹10. Hide two coins in your hand. Tell your friend the total. Can they guess which two coins you have? Check by adding.
Practice
1
2 of these coins make ₹6. Which coins are they?
₹5 and ₹1.
2
2 coins make ₹3. Which coins are they?
₹2 and ₹1.
3
2 coins make ₹12. Which coins are they?
₹10 and ₹2.
4
Two coins make ₹7. One is ₹5. Which coin is hidden?
₹2.
5
Can 2 coins make ₹8? Try.
No. We need 3 coins, such as ₹5, ₹2 and ₹1.