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You should also read the posting on Sarin learns Average Number, Percentage and Charting in school (Math Concept) to understand about Average Number.
You can read the postings on Sarin learns concept of ratio in school to understand the concept of Ratio.
Challenge yourself with the question before look out for the given solution‼!
Upper primary school mathematics question UPQ284
Hairu had twice as many stickers as Sarin at first. After Hairu bought another 20 stickers and Sarin bought another 105 stickers, Sarin had three times as many stickers as Hairu.
(a) How many stickers did Sarin have at first?
(b) Find the average number of stickers the two of them had in the end.
Based on at the end Sarin has 3 times stickers as Hairu
By fitting in also the number of stickers each of them bought and draws the model
Per the model
You can see the green block is equal to 2 purple blocks plus 20
Sarin had 3 times of Hairu at the end
So Sarin had 3 time the purple blocks plus 20 that Hairu had
5 units = 105 – 20 – 20 – 20 = 45
1 unit = 9
Sarin had 9 stickers at first
Total number of stickers together in the end = 3 × 9 + 105 + 20 = 152
The average number of stickers the two of them had at the end = 152 ÷ 2 = 76
Stickers ratio before, Hairu : Sarin = 2 : 1
Hairu bought 20 stickers and Sarin bought 105 stickers
Stickers ratio after, Hairu : Sarin = 1 : 3 = (2U + 20) : (1U + 105)
6U + 60 = 1U + 105
5U = 45
1U = 9
Lisa had 9 stickers at first
Total number of stickers at the end = 3U + 125 = 27 + 125 = 152
The average number of stickers the two girls had at the end = 152 ÷ 2 = 76