Meiosis is a little different than mitosis. In mitosis, you get two cells at the end with the final number of chromosomes still at 40 in each cell. In meiosis, the cells divide twice: once to split up the genes into half, and then again so that each cell has only a quarter of the DNA. So, if the mother cell has 40 chromosomes, then the daughter cells will have 10 each.
Each combination of genes will be different for the daughter cells, but it will still be 10 chromosomes in the end. Meiosis takes a little longer than mitosis for that reason: the mother cell has four cells to produce. Other than that, the process of meiosis does not differ from mitosis.
The answer should be 10. This is because in meiosis, four different daughter cells are produced. So the original number of chromosomes which is 40 is divided by 4 to get 10. If I am wrong, then I am confused on how the answer is 20.