In this question, the mean is 20.2 and the standard deviation is 2.4. That means the range for of 1 standard deviation would be 20.2 +- 2.4= 17.8- 22.6 The number that included in that range would be 18-22. Then you just need to add them all
18 =2 19 =3 20 =4 21 =3 22 =1 The answer would be: 2+3+4+3+1 = 13
