Upper primary school mathematics question UPQ42
Hairu and Sarin shared some stickers. When Hairu gave 20 stickers to Sarin, both of they would have same amount of stickers. If Sarin gave 20 stickers to Hairu, Hairu would have 5 times as many stickers than Sarin. How many stickers did each of them have?
Solution:
When Hairu gave 20 stickers to Sarin, they had an equal amount of stickers. There was 40 stickers difference between them.
The math model,
When Sarin gave 20 stickers to Hairu, Sarin’s stickers reduced from the “White” portion to the “Green” portion. At the same time Hairu got 20 more stickers.
Since, Hairu had 5 times as many stickers than Sarin after received 20 more stickers,
4 times = 4 units = 80 stickers
Hairu had 4 units = 80 stickers
Sarin had 2 units = 40 stickers
Alternative solution:
By guess and check,
Note:
1. Start the guess with stickers more than 20
2. Hairu has more stickers that Sarin
Guess 
Check  Check  
Sarin 
Hairu 
S + 20 
H – 20 

H + 20 
S 20 
Times 

30 
60 
50 
40 
× 



× 
30 
65 
50 
45 
× 



× 
30 
70 
50 
50 
√ 
90 
10 
9 
× 
40 
70 
60 
50 
× 



× 
40 
80 
60 
60 
√ 
100 
20 
5 
√ 
Hairu had 4 units = 80 stickers
Sarin had 2 units = 40 stickers
Wow! That’s an remarkable slant.