PS: Tank Radius - Explaination on solving this equation

[Sunghko]

When a cylindrical tank is filled with water at a rate of 22 cubic meters per hour, the level of water in the tank rises at a rate of 0.7 meters per hour. Which of the following best approximates the radius of the tank in meters?

A. (Sq10)/(5)
B. (Sq10)
C. 4
D. 5
E. 10


Volumecylinder = r2h

1. 22 = r2(0.7) (use ≈ 22/7 )

2. 22 ≈ 22/7 (7/10) r2

3. r2 ≈ 10

4. r ≈

Can someone explain step #1 and step #2 on how they are using pie to divide?

[LazyNK]

Hi Sunghko,

I think there is a typo in following :
Volume = r2*h
It should be Volume= pi*r2*h

So, now you can see how it works.
Every hour, increase in volume is 22 cu.m and corresponds to a height of 0.7m.
-> 22= pi*r2* 0.7
You can use one of the two values of pi viz. 3.14 in case you want to express in decimals or 22/7 in case you find an equation in terms of fractions - Decide based on what you see in equation to be solved. Here , I see 22 on L.H.S, and 0.7 on R.H.S . I should choose pi=22/7 as that would simplify calculations.
-> 22=(22/7)*(r2*0.7)
-> 1= r2/10
-> r=sqrt(10)

Hope it is clear.
-NK

[jnelson0612]

Hi Sunghko,

I think there is a typo in following :
Volume = r2*h
It should be Volume= pi*r2*h

So, now you can see how it works.
Every hour, increase in volume is 22 cu.m and corresponds to a height of 0.7m.
-> 22= pi*r2* 0.7
You can use one of the two values of pi viz. 3.14 in case you want to express in decimals or 22/7 in case you find an equation in terms of fractions - Decide based on what you see in equation to be solved. Here , I see 22 on L.H.S, and 0.7 on R.H.S . I should choose pi=22/7 as that would simplify calculations.
-> 22=(22/7)*(r2*0.7)
-> 1= r2/10
-> r=sqrt(10)

Hope it is clear.
-NK

Wow, again, excellent work!

[LazyNK]

@jamie, no worries :). In fact, I too have learned so much from the strategy guides,specifically in verbals, but still, I do a lot of mistakes under 2 mins pressure :(. Got my GMAT on 12th march, am aiming for 750+, but my practice tests scoreshave ranged from 730 to 770, so am somewhat worried, but one thing is sure, manhattan and u guys rock.

[tim]

Thanks Lazy, and good luck with your continued studying..