Hideko has 3/5 yard of ribbon to tie on balloons for the festival. each balloon will need 3/10 yard of ribbon. how many balloons can hideko tie with ribbon?

In the given question, most of the information's are already provided. Using these information's the required answer can be easily found. Hideko has 3/5 yard of ribbon in total. He needs 3/10 yards of ribbon to tie 1 balloon. It has to be found, the number of balloons Hideko can tie with the total ribbon he has.
Let us assume that the number of balloons Hideko can tie = x
then
3/10 yard of ribbon is required to tie = 1 balloon
3/5 yard of ribbon can be used to tie = (10/3) * (3/5)
                                                           = 2
So Hideko can tie 2 balloons with the total ribbon he has.

Whose mistake? can you give more details to what the question is asking?

I'm sure the answer is a