If both pipes are opened. Then the number of hours to fill up the tank fully is 100 hours.
The complete question is attached below.
What are ratio and proportion?
A ratio is a collection of ordered integers a and b represented as a/b, with b never equaling zero. A proportionate expression is one in which two items are equal.
Let t be the filling time.
Then we have
Time is inversely proportional to rate of filling tank.
1/20 – 1/25 = 1/t
0.05 - 0.04 = 1/t
0.01 = 1/t
t = 1/0.01
t = 100 hours
More about the ratio and the proportion link is given below.
https://brainly.com/question/14335762
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