Question 1149800
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Let the number under the question is "n".


Then the total mass of "n" people is  42*n kilograms.


When the 70-kilo person was added to the group, the mass became  (42*n+70) kilograms;

the number of people in the extended group is (n+1) now.


So your equation is


    {{{(42*n+70)/(n+1)}}} = 46.


To solve the equation, first multiply both sides by (n+1).  You will get


    42*n + 70 = 46*(n+1).


The rest is clear, and I leave it to you to complete the solution on your own.
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