Question

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D?

Answer 1

when the denominators are the same 9 in this case they are 10) you just add the top numbers ( the numerators). The denominators are unchanged.
Then try to find common factors in order to simplify.

Answer 2

the above process gives us 6/10 as you said. but thats not the simplest form.

Answer 3

Hint: the 2 numbers are both even. 2 is a common factor

Answer 4

Is A in simplest form?

Answer 5

3/5 yes