Question 131973
{{{p}}}= number of pigs
{{{c}}}= number of chickens
They all have exactly 1 head, so
(1) {{{p + c = 27}}}
(2) {{{4p + 2c = 78}}}
Multiply (1) by {{{-2}}} and add to (2)
{{{4p + 2c = 78}}}
{{{-2p - 2c = -54}}}
{{{2p = 24}}}
{{{p = 12}}}
{{{12 + c = 27}}}
{{{c = 15}}}
There are 12 pigs and 15 chickens
check:
{{{4p + 2c = 78}}}
{{{4*12 + 2*15 = 78}}}
{{{48 + 30 = 78}}}
{{{78 = 78}}}
OK