Question 1201743
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Answers:
1 liter of water is needed
length = 20 cm


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Work Shown:


x = breadth
2x = length
area of base = length*breadth
area of base = 2x*x
area of base = 2x^2


h = starting height of the water line
volume of water = (area of base)*(height of water line)
volume of water = (2x^2)*(h)
volume of water = 2x^2h


volume of the tank = (area of the base)*(height of the tank)
volume of the tank = 2x^2*30
volume of the tank = 60x^2


When the tank is 1/3 full, there are 2x^2h cubic cm of water.


volume of water = (1/3)*(volume of tank)
2x^2h = (1/3)*(60x^2)
2x^2h = 20x^2
2h = 20
h = 20/2
h = 10


The water line starts off at a height of 10 cm.
The shortcut would be to say (1/3)*30 = 10.


After adding the 3000 cm^3 of water, the height goes to 25 cm. 
Which is an increase of 25-10 = 15 cm.


new amount of water = (area of base)*(change in height)
new amount of water = (2x^2)*(15)
new amount of water = 30x^2


This is set equal to 3000 since we've added this new amount of water.
30x^2 = 3000
x^2 = 3000/30
x^2 = 100
x = sqrt(100)
x = 10
then
2x = 2*10 = 20


The breadth is 10 cm.
The length is 20 cm.
The area of the base is 20*10 = 200 cm^2


The tank is 30 cm tall and we've reached the 25 cm marker
The difference in height is 30-25 = 5 cm.


Let's calculate how much water we need to fill up the rest of the tank.
water needed = (area of the base)*(change in height)
water needed = (200)*(5)
water needed = 1000 cm^3
water needed = 1000 mL
water needed = 1 liter
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