Math Is Fun Forum

sweetgyal1991

Guest

Finding age when given total

Last question today from me... Lucy is 6 years older than Lana and Jo is 5 years older than Lucy and the total of their ages is 41, how old is Lana?

cushydom

Member

Registered: 2008-04-23

Posts: 10

Re: Finding age when given total

lucy=lana+6
jo=lucy+5=lana+6+5=lana+11
41=lana+lana+6+lana+11
3*lana=24
lana=8

sweetgyal1991

Guest

Re: Finding age when given total

whoo! thank you, I was not going to figure that out!

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: Finding age when given total

That was a great way to do it, cushydom!
And here is another way just for kicks (fun)...
la = lu - 6
jo = lu + 5
Make both 5.5 or 5 and a half so they will cancel.
la = (lu - 0.5) - 5.5
jo = (lu - 0.5) + 5.5
Now we have 3 linear things:  la, (lu - 0.5), and jo
la is the smallest, lu - 0.5 is the middle, and jo is the biggest.
Because they "balance" when added, then just
do 3 times the middle one and set it equal to 40.5,
because lu - 0.5 is one-half smaller than it used to be,
so their total is one-half smaller too, so use 40.5 .
40.5 = 3 * (lu - 0.5)
Now 39 / 3 = 13  and 1.5 + 39 = 40.5 and 1.5 / 3 = one-half = 0.5
So lu - 0.5 = 13.5
Hence, lu = 14
jo = 5.5 + 13.5 = 19
la = 13.5 - 5.5 = 8
Same answer, just a different trip.

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