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

Redeem

Would someone explain to me why my method didn't work?

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 86
Joined: Tue Aug 05, 2008 10:50 am
Thanked: 7 times

Would someone explain to me why my method didn't work?

by hengirl03 » Fri Aug 22, 2008 10:18 pm
John's front lawn is 1/3 the size of his back lawn. If John mows 1/2 of his front lawn and 2/3 of his back
lawn, what fraction of his lawn is left unmowed?

1/6
1/3
3/8
1/2
5/8

In order to solve this problem, I picked 12/12 for the area of the back lawn and 4/12 for the front lawn. So, the total area of lawn is 16/12

1/2 of the front lawn = 2/12
2/3 of the back lawn = 8/12

Area of the lawn mowed = 10/12

Unmowed lawn 16-10/12 = 6/12 = 1/2

However, answer is 3/8[/b]
Top
Source: — Problem Solving |
Senior | Next Rank: 100 Posts
Posts: 76
Joined: Sat Aug 02, 2008 10:05 pm
Thanked: 5 times

by rishi235 » Fri Aug 22, 2008 10:35 pm
Well u method is perfect till this step
Unmowed lawn 16-10/12 = 6/12 = 1/2

But u have missed the final step...
The question asks u that what fraction is unmowed

So the ans = Unmowed / Total lawn
=> 1/2 / 16/12
=> 1/2 * 12/16
=> 6/16 => 3/8

So u just missed the last step..

I followed a different approach

Let Back lawn be x
Hence front lawn = 1/3x
Now its given that John mows 1/2 of his front lawn and 2/3 of his back
Hence Back lawn (unmowed) = 1/2*1/3x
Front lawn (unmowed) = 1/3x

Hence [1/2*1/3x+1/3x] / 4/3x
Solving we get 3/8

Hope this helps...
Last edited by rishi235 on Fri Aug 22, 2008 10:40 pm, edited 1 time in total.
Top
Master | Next Rank: 500 Posts
Posts: 172
Joined: Wed Oct 31, 2007 11:21 am
Thanked: 1 times

by gmattester » Fri Aug 22, 2008 10:39 pm
F+B=L
F=1/3B
Unmowed=B/2
Fraction= Unmowed/Total
(B/2) / (4/3B) =3/8
Top
Master | Next Rank: 500 Posts
Posts: 133
Joined: Sat Dec 29, 2007 2:43 am
Thanked: 12 times

by raju232007 » Sat Aug 23, 2008 3:04 am
If you assume data & solve this question you will be able to solve it much quicker than the conventional method that I have described below...

Total lawn(T)=Front Lawn(F) + Back Lawn(B)
Given: F=B/3
then T= 4B/3

Given that 1/2 of the front lawn and 2/3 of the back lawn are mowed...

i.e 1/2(B/3)+2/3(B) = 5B/6
therefore lawn unmowed is given by (4B/3)-(5B/6) = 3B/6 = B/2

Fraction of lawn unmoved is given by (B/2)/(4B/3) = 3/8
Top
User avatar
Legendary Member
Posts: 871
Joined: Wed Aug 13, 2008 7:48 am
Thanked: 48 times

by stop@800 » Sat Aug 23, 2008 4:40 am
Easy explanation
Total = 12

Front = 3
Back = 9

Mowed
Front = 3 / 2 = 1.5
Back = 9 * 2 /3 = 6

Left
Front = 1.5
Back = 3

Fraction
4.5 / 12 = 3/8
Top
Post new topic Post Reply
• Page 1 of 1