IMAS 2017 — Upper Primary Grades 5–6 — Round 1 Question 6

On a $5\times5$ table below, place into each cell the sum of its row number and column number. For example, value of a below is $2+3=5$ . How many odd numbers are filled into the table?
|Row/Column|1|2|3|4|5|
|---|---|---|---|---|---|
|1| | | | | |
|2| | |a| | |
|3| | | | | |
|4| | | | | |
|5| | | | | |