There are a number of different problems that you could do that will give you an outcome of 9/10
For example, 1/2 and 2/5 add up to 9/10.
3/10 and 6/10 also add up to 9/10.
Find the sum of 7/10 and 1/5
Find the sum of 7/20 and 11/20
Find the sum of 1/2 and 3/10 and 1/10
Find the sum of 1/5 and 2/5 and 3/10
Hope this helps :)