Another way to
write the problem in the Challenge, where x
is the
weight of the little fish,
y is the weight
of the medium fish,
and z
is the weight of the big fish,
is:
x
+ y = 5
y
+ z = 7
x
+ z = 6
As a young woman, Mary
Fairfax Somerville (1780–1872) discovered
algebra
while reading a ladies’ fashion magazine. In its
pages, she saw a question with ”strange looking lines
mixed with letters, chiefly X’s and Y’s”
(Perl, 1978). She continued to study mathematics until
she was 92. 

The National
Council of Teachers of Mathematics (NCTM) recommends
that algebraic thinking start in prekindergarten
using concrete, pictorial, verbal, and symbolic representations.
Spreadsheet
formulas require algebra.
Some formulas
are found in popular reading materials. For example, the
formula for Body Mass Index
(BMI) is found in The Old Farmers’ Almanac (2000).
(See Challenge 21) 