Data Sufficiency

OA: E

My Answer: C

My Explanation:
Say, total gallons of water in tank X = a
Total gallons of water in tank Y = b
Rate of draining of water from tank X = r1
Rate of draining of water from tank Y = r2

Time taken of draining water from both tanks is same hence
a/r1 = b/r2
Also, a = b + 30
We have to find the time to drain i.e either value of a/r1 or b/r2

1) r1 = 2 * r2
So the equation becomes,
(b+30)/2 * r2 = b/r2
We can solve it to find that, a = 45 and b = 15.
But we don’t know r1 or r2 hence INSUFFICIENT
2) r2 = 20 gallons/hr
So the equation becomes,
(b+30)/r1 = b/20
INSUFFICIENT

Together, we know b = 15 and r2 = 20 hence time will be 15/20 hrs. Hence (C)

Case A:
========
(a+30)/2=a/1 which means a=30 (y) and b=60 (x)

Case B:
=====
Alone is no good.

Time = 30/20 = 1hr 30 min

Anybody with fresh ideas?
I ve got C, too.

@devajyothi2000

The OA is C not E. But your working is incorrect.

1 Just gives a ratio of Y and X speed: Y:X=1:2---insuff
2 Just gives Y rate. There is no information about X----insuff

Combining 1&2

Let quantity of water in Y be 'a'
y=a
x=a+30

X's rate = (a+30)/40
Y's rate = a/20

Hence time taken: (a/20)=(a+30)/40

Solving you get a=30
Time taken is 1hr 30mins.

hence C is suff.