Answer:
4
Explanation:
1. Find the Mean
(8+12+15+17+18)/5=14
2.For each number, subtract the Mean and square the result.
(8-14)^2=36
(12-14)^2=4
(15-14)^2=1
(17-14)^2=9
(18-14)^2=16
3. Find the Mean of those squared differences.
(36+4+1+9+16)/5=13.2
4.Take the square root of that and this is what you want.
square root of 12.7 = 3.6 (round up to 4)