To find the mean of a data set all you need to do is add up the numbers in the data set and divide by the number of numbers in the data set. So if the data set is (2,4,6,8,10,12) then you would do 2+4+6+8+10+12=42, then divide by the amount of numbers in that set, in this case the number is 6. So divide 42 by 6 and you get 7, so the mean equals 7.
In your case they try to make it more difficult by excluding certain numbers, what you have to do is make sure you keep track of the numbers you exclude.
1.) Find the mean of the data set excluding numbers ending with 0 between 1-20. Those numbers are: 1, 2,3,4,5,6,7,8,9,11,12,13,14,15,16,17,18,19. Remember that you left out 2 numbers, 10 and 20. Add you data set together to get 180. Now you need to divide 180 by the amount of numbers, remember there are 2 less numbers than 20 so that is 18, 180 divided by 18 is 10.
2.) You will do the same thing for every problem, I will walk you through this one and do a few more but the rest is up to you. This question asks you to: find the mean of the data set excluding numbers with the last digit 2 between 1-10. List all of the numbers not ending in 2 between 1-10: 1,3,4,5,6,7,8,9,10. Add all of those numbers together: 53. Divide 53 by the amount of numbers in the data set, in this case, 9. 53 divided by 9 is 5.888888888888889 or 5.89.
3.) This question asks you: find the mean of the data set excluding numbers with last digit 5 between 1-20. In this case you will be excluding 5 and 15, that is 2 numbers. Add up: 1,2,3,4,6,7,8,9,10,11,12,13,14,16,17,18,19,20. You will get: 190, divide that by 18 to get: 10.55555555555556 or 10.56.
4.) This question asks you: find the mean of the data set using numbers between 1-20. So add up: 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20. You will get: 210. Divide 210 by the total number of numbers which is 20, the answer is: 10.5.
5.) This question asks you: find the mean of the data set excluding numbers ending with the last digit 1 between 1-10. So add up the numbers between 1 and 10, excluding 1 and 10: 2,3,4,5,6,7,8,9 to get: 44. since you took out 2 numbers divide by 8, 44 divided by 8 is 5.5.
I hope this helped, if you need any further help, just ask. :)
