Question: 210 210 220 245 260 what number do you need to get the mean of 235 ?
At the moment you have 5 numbers.
If you had 6 numbers and their mean was 235, then their sum would be 6*235 = 1410.
The sum of your 5 numbers is 210 + 210 + 220 + 245 + 260 = 1145.
To get a sum of 1410, you would need to add on 265 to 1145.
So the 6th number needed is: 265