Question 408217
A heads and legs problem:

A farmer has chickens and cows. He counts 40 heads and 86 legs
How many chickens and cows does he have?
Let {{{c}}} = number of chickens
Let {{{m}}} = number of cows
-------------------------
given:
(1) {{{c + m = 40}}} (all have just 1 head)
(2) {{{2c + 4m = 86}}}
----------------
This is 2 equations and 2 unknowns, so it's solvable
from (2):
{{{c + 2m = 43}}}
{{{c = 43 - 2m}}}
By substitution:
{{{43 - 2m + m = 40}}}
{{{m = 3}}}
and
{{{c + m = 40}}}
{{{c = 40 - 3}}}
{{{c = 37}}}
There are 3 cows and 37 chickens
Check answer:
(2) {{{2c + 4m = 86}}}
{{{2*37 + 4*3 = 86}}}
{{{74 + 12 = 86}}}
{{{86 = 86}}}
OK