The flask contains a 40% acid solution. The volume of the solution was increased threefold

The flask contains a 40% acid solution. The volume of the solution was increased threefold by adding acids there. What is the percentage concentration of the solution?

The flask contains one (1) whole volume of solution.
If the flask contains a 40% acid solution, this means that in the solution 0.4 part of the volume is acid and 0.6 part of the volume is water:
1) 1 – 0.4 = 0.6 (volume) water.

The volume of the solution was increased threefold by adding acids. This means that the flask now contains 3 initial volumes of solution:
2) 1 * 3 = 3 (volume) total has become

Because only acid was added to the solution, then in these three volumes, 0.6 remained of water, and the acid began to occupy 2.4 parts:
3) 3 – 0.6 = 2.4 (volume) acid has become.

Only 3 volumes of solution, and in them 2.4 volumes of acid, which means the concentration of the solution was:
4) (2.4 / 3) * 100% = 80 (%)

Answer: 80%.