algebra problem solving question gcse

Question

I need help on this algebra word problem as I don't know how to work out the number of stamps and I dont know how to approach this question

 

Question:

 

Four boys Alex, Bryan, Calvin and Derrick, each have some stamps. The number of stamps Alex has is
1/2 of the total number of stamps Bryan, Calvin and Derrick have. The number of stamps Bryan has is 
1/3 of the total number of stamps Alex, Calvin and Derrick have. The number of stamps Calvin has is 1/4 of the total number of stamps Alex, Bryan and Derrick have. If Derrick has 78 stamps, find the total number of stamps Alex and Bryan have altogether.

 

Thank You and help is appreciated.

Answer 1

A = (1/2)(B + C + D) ⇒ 2A = B + C + D

B = (1/3)(A + C + D) ⇒ 3B = A + C + D
C = (1/4)(A + B + D) ⇒ 4C = A + B + D

D = 78

 

Substitute 78 for D. Solve the three equations in three variables