Answer: After 20 days
Step-by-step explanation: you have to find the greatest common multiple so that the number is a multiple for each of them
since 10 is multiple of 5 you have to find the lcm of 10 and 4 or 5 and 4 which is still 20
so just multiply them and if she swims and does cycles every 10 days then you know that if she is swimming she is cycling, but if she is cycling she might not be swimming. So if running is 4 days then just multiply 4*5 = 20