right way to explain this question please.
Moderators: Section Moderators, Forum Moderators
right way to explain this question please.
could somebody please explain the right way to show my dd this question thanks.
When i was born my aunt was 21 years old.At my next birthday my aunt will be four times as old as i will be. How old will i be at my next birthday.
I know the answer is seven but i need to find a quicker way to show my dd.
When i was born my aunt was 21 years old.At my next birthday my aunt will be four times as old as i will be. How old will i be at my next birthday.
I know the answer is seven but i need to find a quicker way to show my dd.
This is how I would do it:
'my age' + 21 = 'my aunt's age'
so
'my aunt's age' - 'my age' = 21
In addition,
'my aunt's age' = 'my age * 4
Replace 'my aunt's age' with 'my age' * 4 in
'my anount's age' - 'my age' = 21
You get
'my age' * 4 - my age = 21
so
'my age' * 3 = 21
'my age' = 7
Hope this helps
Catherine
'my age' + 21 = 'my aunt's age'
so
'my aunt's age' - 'my age' = 21
In addition,
'my aunt's age' = 'my age * 4
Replace 'my aunt's age' with 'my age' * 4 in
'my anount's age' - 'my age' = 21
You get
'my age' * 4 - my age = 21
so
'my age' * 3 = 21
'my age' = 7
Hope this helps
Catherine
-
- Posts: 1245
- Joined: Fri Jul 06, 2007 9:31 pm
Re: right way to explain this question please.
Age next B'Day N; Aunt will have aged by N years... so age will be 21+N0505 wrote:i need to find a quicker way to show my dd.
N = ( 21 + N ) / 4
4N = 21 + N
3N = 21
N = 7
Potentially a confusing question. Definitely worth checking the answer by substituting back.
Animis opibusque parati
The answers given above all use algebra, which is great, but isn't usually the way 11 year olds think (at least those from state schools). Kids on the other hand are usually very good at working out how old someone will be when they are a few years older. I would expect my 11 year old to scribble out the following to solve this problem:
Me Aunt
0 21
1 22
2 23
3 24
4 25
5 26
6 27
7 28
This takes only a few seconds, and the answer leaps out.
Hilda
Me Aunt
0 21
1 22
2 23
3 24
4 25
5 26
6 27
7 28
This takes only a few seconds, and the answer leaps out.
Hilda
I agree with Hilda. While the other methods are sound algebraically, trial and error would probably produce a quicker answer, especially if they have a 'feel' for maths and could make a decent initial guess which they would then adjust. I have some old Maths Challenge books I use (out of print) and they positively encourage guessing, but in an orderly fashion by drawing a quick little table.If you're exam in multiple choice, then you'd want to go for substitution of answers.