Model Method - Questions and Answers
Question posted by Christina from Singapore:Grade/Level: Primary 5 Question solved by "Working Backwards" Heuristics: Jasmine and David have a certain number of stickers. Jasmine gave 1/5 of her stickers to David. David then gave 1/6 of what he had to Jasmine. After that, Jasmine gave 18 stickers to David. In the end, Jasmine had 36 stickers and David had 88 stickers. How many stickers did Jasmine have at first?
Answer:
Step 1: Draw a simplified table to show the number of stickers Jasmine and David had which is 36 and 88 respectively.
Step 2: Since we are working backwards, we should undo the last action. As Jasmine had given 18 stickers to David, we should make David return the 18 stickers to her. So we subtract 18 from David and add 18 to Jasmine.
Step 3: That leaves Jasmine with 54 and David with 70.
Step 4: Since David had given 1/6 of what he had to Jasmine, he should have 5/6 of what he had left. Thus, 70 should be equivalent to 5/6.
Step 5: If 70 is equivalent to 5/6, then 1/6 should be equivalent to 14. So we add 14 back to David and subtract 14 from Jasmine.
Step 6: That leaves Jasmine with 40 and David with 84.
Step 7: Since Jasmine had given 1/5 of what she had to David, she should have 4/5 of what she had left. Thus, 40 should be equivalent to 4/5.
Step 8: If 40 is equivalent to 4/5, then 1/5 should be equivalent to 10. So we add 10 back to Jasmine and subtract 10 from David.
Step 9: That leaves Jasmine with 50 and David with 74.
Therefore, Jasmine had 50 stickers at first.
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