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PostPosted: Sat Dec 20, 2014 3:44 pm 
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Joined: Fri Nov 28, 2014 10:02 pm
Posts: 5
The ages of Grandma, Aunt Jane and Sara add up to 119 years. Grandma is twice as old as Aunt Jane, and Aunt Jane is twice as old as Sara.
Grandma is years old, Aunt Jane years old and Sara is years old.


The answer is 17, 34 and 68

But how shall we do the calculation

Please help


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PostPosted: Sat Dec 20, 2014 3:52 pm 
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Joined: Mon Feb 12, 2007 1:21 pm
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Grandma is twice as old as Aunt Jane, and Aunt Jane is twice as old as Sara.

So, trying to avoid using algebra, think about each person's age in terms of Sara's.

Aunt Jane = two Sara

Grandma = two Aunt Jane = .... Sara

Then we know the total, so add them all up.

I do not agree with posting full solutions as that won't help you another time.


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PostPosted: Sat Dec 20, 2014 9:14 pm 
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Joined: Mon Sep 10, 2012 8:44 pm
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I would do it like this:
Sara is the youngest, so call her age X years
Aunt Jane is twice Sara's age, i.e. 2X
Grandma is twice Aunt Jane's age, i.e. 4X

Total of ages: X + 2X + 4X = 7X
7X = 119
X = 119/7 = 17


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PostPosted: Sat Dec 20, 2014 9:20 pm 
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It's better for the OP if full solutions are not posted ...


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PostPosted: Sun Dec 21, 2014 10:27 pm 
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Joined: Fri Oct 12, 2007 12:42 pm
Posts: 3817
Location: Chelmsford and pleased
I would bar model. The strips are a stunning aid in proportional reasoning questions. Hard to communicate on here, but quick and simple to draw and give children a visual aid and no need for algebra.

Start with Sara and draw a block.
---
Then draw two blocks the same size, Jane.
------|---
Next draw two Jane sized blocks (4 Sara blocks).
------|------|---|---|---
You now have one strip comprised of 7 Sara sized blocks. The total ages are the whole strip, so divide by 7 to give Sara.


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