Answer:
4/21
Explanation:
first you need to make them both fractions, not mixed numbers. so it would be 2/5 divided by 21/10. then you flip the second number so you can multiply it : 2/5 * 10/21. 5 and 10 are divisible by 5 so you can cross 5 out and make a 1 and cross 10 out and make a 2: 2/1 * 2/21. then multiply and you get 4/21!
hope this helps!