Given that the ratio of three trays is A : B : C = 2 : 3 : 4
Let us consider the common factor among the number of trays be "x".
If we need to make a total of 171 trays, then the equation of sum of trays would be :-
Type A + Type B + Type C = 171
2x + 3x + 4x = 171
9x = 171
x = = 19
So we have following number of trays :-
Number of type A trays = 2x = 38 trays.
Number of type B trays = 3x = 57 trays.
Number of type C trays = 4x = 76 trays.
Now if each tray contains 20 cookies, then we would have following arrangements :-
Cookies in type A trays = 38×20 = 760 cookies.
Cookies in type B trays = 57×20 = 1140 cookies.
Cookies in type C trays = 76×20 = 1520 cookies.