2019 Math Kangaroo Levels 9-10 Problem #28

2019 Math Kangaroo Levels 9-10 Problem #28 28. What is the least number of elements we have to delete from the set below so that the product of the elements remaining in the set is a perfect square ? {10, 20, 30, 40, 50, 60, 70, 80, 90} (A) 1 (B) 2 (C) 3 (D) 4 (E) 5 Thank you for watching and please like, comment, and subscribe!