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Primary 3 | Maths
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Need help! Couldn’t understand to explain to my p3 kid. Thanks much!
Date Posted: 3 years ago
Views: 503
This is a 'difference unchanged' question
Age differences don't change since everyone's chronological age increase at the same rate.
Eg.
Lets say there are two people.
Person A is 12 years old and Person B is 7 years old. Their age difference is 5 years. (12 - 7 = 5)
1 year later, Person A will be 1 year older. Person A is now 13 years old.
Person B will also be 1 year older. Person B is now 8 years old.
Because they both aged by 1 year, their age difference is unchanged. It is still 5 years.
(13 - 8 = 5)
So for Sebastian and Garrett,
in 10 years time they will both be 10 years older.
Their age difference is still unchanged at 24 years.
Since Garrett will be thrice as old as Sebastian in 10 years' time,
we let Garrett's age in 10 years' time be 3 units and Sebastian's age in 10 years' time be 1 unit.
Age Difference = 3 units - 1 unit = 2 units
2 units = 24 years
1 unit = 24 years ÷ 2 = 12 years
Eg.
Lets say there are two people.
Person A is 12 years old and Person B is 7 years old. Their age difference is 5 years. (12 - 7 = 5)
1 year later, Person A will be 1 year older. Person A is now 13 years old.
Person B will also be 1 year older. Person B is now 8 years old.
Because they both aged by 1 year, their age difference is unchanged. It is still 5 years.
(13 - 8 = 5)
So for Sebastian and Garrett,
in 10 years time they will both be 10 years older.
Their age difference is still unchanged at 24 years.
Since Garrett will be thrice as old as Sebastian in 10 years' time,
we let Garrett's age in 10 years' time be 3 units and Sebastian's age in 10 years' time be 1 unit.
Age Difference = 3 units - 1 unit = 2 units
2 units = 24 years
1 unit = 24 years ÷ 2 = 12 years
So,
Garrett's age in 10 years time
= 3 × 12 years
= 36 years
Garrett's age now
= 36 years - 10 years
= 26 years
Garrett's age in 10 years time
= 3 × 12 years
= 36 years
Garrett's age now
= 36 years - 10 years
= 26 years
Check : Sebastian's age now
= 26 years - 24 years = 2 years
Sebastian's age in 10 years time
= 2 years + 10 years
= 12 years
36 is thrice of 12 (12 × 3 = 36)
So this fits the question info that Garrett will be thrice as old as him in 10 years' time.
= 26 years - 24 years = 2 years
Sebastian's age in 10 years time
= 2 years + 10 years
= 12 years
36 is thrice of 12 (12 × 3 = 36)
So this fits the question info that Garrett will be thrice as old as him in 10 years' time.
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See question's comments section for explanation
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Key is to draw the model out and visually understand that Garrett is thrice Sebastian’s age, which works out the ratio of 1:3 within the model.
Although he is three times older, the difference is the same which is 24 years (equivalent to 2 units in the model).
Thus, divide that by two to find out how many years is one unit. Hope this helps!
Although he is three times older, the difference is the same which is 24 years (equivalent to 2 units in the model).
Thus, divide that by two to find out how many years is one unit. Hope this helps!
Date Posted:
3 years ago
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Date Posted:
2 years ago
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