Reservoir A contains 450 million gallons of water more than does Reservoir B. If 100 million gallons of water were...

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BTGmoderatorLU: Moderator; Posts: 2650; Joined: Sun Oct 15, 2017 1:50 pmFollowed by: 6 members

by BTGmoderatorLU » Fri Apr 03, 2020 2:42 am

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Source: Princeton Review

Reservoir A contains 450 million gallons of water more than does Reservoir B. If 100 million gallons of water were to be drained from Reservoir A into Reservoir B, then Reservoir A would contain twice as much water as would Reservoir B. How many million gallons of water does Reservoir A currently contain?

A. 500
B. 600
C. 700
D. 800
E. 900

The OA is C

Source: Beat The GMAT — Problem Solving | Fri Apr 03, 2020 2:42 am

deloitte247: Legendary Member; Posts: 2214; Joined: Fri Mar 02, 2018 2:22 pmFollowed by: 5 members

Re: Reservoir A contains 450 million gallons of water more than does Reservoir B. If 100 million gallons of water were..

by deloitte247 » Sun Apr 05, 2020 8:19 am

How many million gallons of water does Reservoir A currently contain?
Solution:
A = 450 + B ------ eqn (1)
A - 100 = 2 (B + 100)
A - 100 = 2B + 200
A = 2B + 300 ------ eqn (2)
Substitute the value of A in eqn (1) with A in eqn (2)
450 + B = 2B + 300
450 - 300 = 2B - B
B = 150
Substitute the value of B in eqn (2) with the exact value of B
A = 2B + 300
A = 2(150) + 300
A = 600

Answer = Option B

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Re: Reservoir A contains 450 million gallons of water more than does Reservoir B. If 100 million gallons of water were..

by Scott@TargetTestPrep » Thu Apr 09, 2020 3:50 am

BTGmoderatorLU wrote: ↑
Fri Apr 03, 2020 2:42 am
Source: Princeton Review

Reservoir A contains 450 million gallons of water more than does Reservoir B. If 100 million gallons of water were to be drained from Reservoir A into Reservoir B, then Reservoir A would contain twice as much water as would Reservoir B. How many million gallons of water does Reservoir A currently contain?

A. 500
B. 600
C. 700
D. 800
E. 900

The OA is C

We can create the equations:

A = 450 + B

and

A - 100 = 2(B + 100)

A - 100 = 2B + 200

A = 2B + 300

Substituting, we have:

450 + B = 2B + 300

150 = B

So A = 450 + 150 = 600.

Answer: B

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