Answer:
A large box weighs 18.5 kilograms and a small box weighs 15.5 kilograms
Step-by-step explanation:
Create a system of equations where l is the weight of one large box and s is the weight of one small box.
2l + 12s = 223
5l + 3s = 139
Solve by elimination by multiplying the bottom equation by -4:
2l + 12s = 223
-20l - 12s = -556
Add these together and solve for l:
-18l = -333
l = 18.5
So, a large box weighs 18.5 kilograms. Plug in 18.5 as l into one of the equations, and solve for s:
5l + 3s = 139
5(18.5) + 3s = 139
92.5 + 3s = 139
3s = 46.5
s = 15.5
A large box weighs 18.5 kilograms and a small box weighs 15.5 kilograms.
9514 1404 393
Answer:
Step-by-step explanation:
Two equations for the total weight can be written in general form as ...
2L +12S -223 = 0
5L +3S -139 = 0
These can be solved using the "cross multiplication method" by computing three differences:
d1 = (2)(3) -(5)(12) = 6 -60 = -54
d2 = (12)(-139) -(3)(-223) = -1668 +669 = -999
d3 = (-223)(5) -(-139)(2) = -1115 +278 = -837
Then the weighs of the boxes are ...
1/d1 = L/d2 = S/d3
L = d2/d1 = -999/-54 = 18.5
S = d3/d1 = -837/-54 = 15.5
The large box weighs 18.5 kg; the small box weighs 15.5 kg.
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Additional comment
If the coefficients are written in two rows of four numbers, with the first repeated at the end, the pattern of differences can be seen to be (ad -cb) for [a, b] in the first row and [c, d] in the second row of a pair of adjacent columns. This method of solution is fully equivalent to solution using Cramer's Rule for a system of equations represented by a matrix equation.
