Question 563890
let the number in the group be x

total mass = x*45.2 =45.2x

One person joins so the total mass = 45.2x+ 51

The number of people = x+1

Average of the group ={{{(45.2x+51)/(x+1)=45.2+0.2}}}


={{{(42.5x+51)/(x+1)=45.4}}}

45.4(x+1)=45.2x+51

45.4x+45.4=45.2+51

45.4x-45.2x=51-45.4
0.2x=5.6
/0.2
x=28

there are 29 in the group now