To find the class mark (xi​) for each interval, using the following relation:(xi​)=2Upper  class  limit+Lower  class  limit​Class size, h, of this data =3Considering 75.5 as assumed mean (a),di​,ui​,fi​ui​ are calculated as follows:From the table:∑fi​=30∑fi​ui​=4Mean, xˉ=a+( ∑f i​ ∑fi​ui​ ​ )×h=75.5+4/30×3=75.5+0.4=75.9∴ mean heart beats per minute for these women are 76 beats per minute.