Step-by-step explanation:
we find the average height of each height first,
t¹= (120+124)/2
=244/2
=122
t²= (124+128)/2
t²= 252/2
t²= 126
t³= (128+132)/2
t³= 260/2
t³= 130
t⁴= (132+136)/2
t⁴= 268/2
t⁴ =134
t⁵= (136+140)/2
t⁵= 276/2
t⁵= 138
so multiplying each height by its frequency we can find the total height, so we have..
total height= (122*7)+(126*8)+(130*13)+(134*9)+(138*3)
= 854+1008+1690+1206+414
= 5172
mean height = total height/total frequency
= 5172/40
=129.3
