Math Question Help

[Herts Mum]

Question is :- 12yrs ago, i was exactly a quarter of the age of my older sister. My brother, who is older than my sister, is 20 now. How old will i be in 3 years?


Please explain the answer!

[Guest55]

What a great question - not!

Let my age be m [me!]

NOW
I am m, my brother 20, my sister m + d [she's older than me my d years]

Twelve years ago I was m-12, and my sister m+ d -12

so, m-12 = (m+d-12)/4 a quarter of her age

giving 3m = 36 + d

I can't be less than 13 so try m = 13 giving d =3

DOES IT WORK me 13, brother 20, sister 16

If I take m= 14 sister will be same age as brother [not allowed]

So in three years I will be 16 -

I think it's easier to guess or trial and improvement as teachers call it.

My age can't be less than 13 or twelve years ago I would be zero and the think about 'being a quarter' wouldn't work.

Guess me = 13 sister is (13-12)x 4 then add 12 to get her age now 16

so three ages me = 13, brother =20, sis = 16

If I was 14 sister is (14-12)X 4 + 12 = 20 SAME AGE as brother which is not allowed.

Hope this helps!!!

[Mike]

Hi

I think the original ages were 1, 4 and 8

Making brother 8 + 12 = 20 which works

Sister must have been a multiple of 4 i.e 4, 8, 12. She could not have been 8 or 12 because she is younger than the older brother. So she must have been 4. Making him one year old.

Therefore if he was one twelve years ago he is 13 now and will be 16 in 3 years time.

Regards

[Herts Mum]

Thank you both for your help.