4.
The farmer has 40 more chickens than cows
Ten fewer pigs than cows
Twenty fewer sheep than chickens
Four horses
The total animals in the farm are 110.
First symbolize the expressions, for this I'm going to use the following letters:
x= cows
y=chickens
z=pigs
w=sheeps
u= horses
"The farmer has 40 more chickens than cows"→ y=x+40
"Ten fewer pigs than cows"→ z=x-10
"Twenty fewer sheep than chickens"→ w= y-20
"Four horses"→ u=4
Total animals on the farm:
T=x+y+z+w+u
T=110
As you can see there are 4 unknowns in the equation, considering that x is the one most repeated, first thing is to express all the others in terms of it.
Using y=x+40, I'll rewrite the formula for w in terms of x:
w=y-20
w=(x+40)-20 \You can take the parenthesis away
w=x+40-20
w=x+20
Now you have to replace each one on the formula for T
T=x+y+z+w+u
110=x+(x+40)+(x-10)+(x+20)+4
There are 14 cows in the farm.
Next you can calculate the rest of the animals.
Chickens:
y=x+40= 14+40= 54 chickens
Pigs
z=x-10=14-10= 4 pigs
Sheep
w=x+20= 14+20= 34 sheep