Step 1:

Standard deviation of the grouped frequency distribution:

where

Ages	Mid point ()	Frequency()
20-29	24.5	27	661.5	-11.341	3472.977
30-39	34.5	34	1173	-1.341	61.184
40-49	44.5	13	578.5	8.659	974.613
50-59	54.5	2	109	18.659	696.282
60-69	64.5	4	258	28.659	3285.247
70-79	74.5	1	74.5	38.659	1494.482
80-89	84.5	1	84.5	48.659	2367.653
Total	-			-

Standard deviation:

Standard deviation : 12.3490.

Solution:

Standard deviation of the grouped frequency distribution is 12.3490.

Step 1:

Standard deviation of the grouped frequency distribution:

where

IQ score	Mid point ()	Frequency()
50-59	54.5	4	218	-30.165	3639.779
60-69	64.5	10	645	-20.165	4066.389
70-79	74.5	25	1862.5	-10.165	2583.328
80-89	84.5	43	3633.5	-0.165	1.175
90-99	94.5	26	2457	9.835	2514.76
100-109	104.5	8	836	19.835	3147.326
110-119	114.5	3	343.5	29.835	2670.33
120-129	124.5	2	249	39.835	3173.608
Total	-			-

Standard deviation:

Standard deviation : 13.477.

Solution:

Standard deviation of the grouped frequency distribution is 13.477.