BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Age Problem Differences

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 114
Joined: Mon Oct 20, 2008 7:03 pm
Thanked: 4 times
Followed by:5 members

Age Problem Differences

by jnellaz » Wed Nov 19, 2008 7:13 pm
Can someone assist with the following two problems? According to the text, Problem 1 only has one unknown while Problem 2 has two unknowns. Thus the approaches were different. To me, I can't tell the difference. Could someone explain how they would approach these problems and whether your approach for each would have one unknown or two? Thanks!

Problem 1:
Sid is twice as old as Rex. Ten years ago, Sid was four times as old as Rex. How old is Sid today?

[spoiler]Answer: 30[/spoiler]


Problem 2:
Joan is 4 times the age of Ben. In 4 years, Joan will be 2.5 times the age of Ben. Ben will be how many years old ten?


[spoiler]Answer: 8[/spoiler]
Top
Source: — Problem Solving |
Legendary Member
Posts: 2467
Joined: Thu Aug 28, 2008 6:14 pm
Thanked: 331 times
Followed by:11 members

by cramya » Wed Nov 19, 2008 7:24 pm
I would solve with just 1 variable for both. Please see attachment.

Hope this helps and let me know if u still have questions.
Attachments
age.xls
(13.5 KiB) Downloaded 203 times
Top
Master | Next Rank: 500 Posts
Posts: 114
Joined: Mon Oct 20, 2008 7:03 pm
Thanked: 4 times
Followed by:5 members

by jnellaz » Wed Nov 19, 2008 7:46 pm
Thank you very much, Cramya!
Top
User avatar
Senior | Next Rank: 100 Posts
Posts: 35
Joined: Wed Oct 01, 2008 3:55 pm
Thanked: 6 times

by rmpaes » Wed Nov 19, 2008 7:51 pm
Sid is twice as old as Rex. Ten years ago, Sid was four times as old as Rex. How old is Sid today?
Let S = Sid's age
Let R = Rex's age

we can get 2 equations by translating the English into math:
now:
(i)S = 2R
ten years ago:
(ii)S-10=4(R-10)

i)S = 2R
ii)S = 4R - 40 +10 [manipulate eq ii]



2R = 4R - 30 [substitute S= 2R into eq ii]
2R = 30
R = 15
i)S = 2(15) = 30
Joan is 4 times the age of Ben. In 4 years, Joan will be 2.5 times the age of Ben. Ben will be how many years old then?
Let J = Joan's age
Let B = Ben's age

now:
(i) J = 4B

four years in future:
(ii) J + 4 = 2.5(B + 4)

2J + 8 = 5(B + 4) [multiply eq ii by 2]

8B + 8 = 5B + 20 [substitute J=4B into eq ii]
3B = 12
B = 4
We want to know Ben's age in 4 years
B+ 4 = 8
700+ your target then check out my 800 gmat blog here:
https://800gmatblog.zoxic.com
Top
User avatar
Legendary Member
Posts: 2134
Joined: Mon Oct 20, 2008 11:26 pm
Thanked: 237 times
Followed by:25 members
GMAT Score:730

Re: Age Problem Differences

by logitech » Wed Nov 19, 2008 8:10 pm
A = 3 years old

B = 7 years old

So B is 4 years older than A

what happens in 5 years ?

A = 3 + 5

B = 7 + 5

B is still 4 years than A.

This sounds silly right ? This is where most of the people make mistakes in ages question.


Now the sum of their age is 3+7 = 10

how about in 5 years ?

10 + 2x(5) = 20

how about 2 years ago

10 - 2x(2) = 6

Take away:

The difference between people's age does not change over the time!

And two people in X years , will have 2X years of addition to their age's sum.
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
Top
Master | Next Rank: 500 Posts
Posts: 114
Joined: Mon Oct 20, 2008 7:03 pm
Thanked: 4 times
Followed by:5 members

by jnellaz » Thu Nov 20, 2008 6:52 am
Rmpaes, thanks again for your approach!
Logitech, as always...great insight! You're the man, behind the man!
Top
Post new topic Post Reply
• Page 1 of 1