A tank was 1/3 full of water. After 2950 ml of water were added, the tank was 3/4 full of water. Find the capacity of the tank in litres.
Let's start by determining what fraction of the tank was filled with water after 2950 ml were added.
We know that the tank was initially 1/3 full. This means that 2/3 of the tank was empty.
After adding 2950 ml of water, the tank was 3/4 full, which means that 1/4 of the tank was empty.
So, we can say that 2/3 + 1/4 of the tank was filled with water after adding 2950 ml.
To find a common denominator, we multiply 2/3 by 4/4 to get 8/12.
Therefore, 8/12 + 1/4 = 10/12 = 5/6 of the tank was filled with water after adding 2950 ml.
Since we know that this amount corresponds to 2950 ml, we can set up a proportion to find the total capacity of the tank.
5/6 = 2950/x, where x is the total capacity of the tank in milliliters.
Cross-multiplying, we get 5x = 6 * 2950.
Simplifying, we obtain 5x = 17700.
Dividing both sides by 5, we find that x = 3540.
So, the capacity of the tank is 3540 ml.
To convert this to liters, we divide by 1000, since 1 liter is equal to 1000 ml.
Therefore, the capacity of the tank is 3540/1000 = <<3540/1000=3.54>>3.54 liters.
Thus, the capacity of the tank is 3.54 liters. Answer: \boxed{3.54}.