SOLUTION: 3 similar chocolate bars and 4 similar packets of candy weigh 200 g. 3 such chocolate bars and 7 such packets of candy weigh 260 g. What is the weight of a chocolate bar?

Let weight of a chocolate bar, and a packet of candy, be B, and C, respectively

Then we get: 3B + 4C = 200 ------ eq (i)

Also, 3B + 7C = 260 ------ eq (ii)

3C = 60 ------ Subtracting eq (i) from eq (ii)

Weight of a chocolate bar, or 

Substitute 20 for C in either eq (i) or eq (ii) and solve for B to get the weight of a chocolate bar.



If you love to TORMENT yourself, then you can do the problem the way the other person did. 

I have no idea why she continues to make MOUNTAINS out of MIOLEHILLS with these simple-enough math problems. 

Looking into the text, an attentive reader sees that


    - the difference between two purchases is 3 packets of candy

    - and the difference in weights between two purchases is 260-200 = 60 grams.


Hence, the weight of one packet of candy is   60/3 = 20 grams.


From it, the weight of 3 chocolate bars is  200 - 4*20 = 120 grams.


Hence, each chocolate bar weights  120/3 = 40 grams.