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Peter counted 9 dogs and cows. He counted 10 cows and goats. He counted 16 animals in all. How many cows in all? Please show the solution.

Sagot :

Shinalcantaraidn
let 'x' be the number of dogs
    'y' be the number of cows
    'z' be the number of goats
x + y = 9   -----equation 1
y + z = 10 -----equation 2
x + y + z = 16 ----equation 3
from equation 1
x + y = 9
x = 9 - y   -----equation 1'
from equation 2
y + z = 10
z = 10 - y  ----equation 2'
substitute equations 1' and 2' to equation 3
x + y + z =16
(9 - y) + y + (10 - y) = 16
9 - y + y + 10 - y = 16
-y = 16 - 9 -10
-y = -3
y = 3 cows
substitute to equations 1' and 2'
x = 9 - y
x = 9 - 3
x = 6 dogs
z = 10 - y
z = 10 - 3
z = 7 goats
Dojonosidn
Add the sum of dogs and cows to the sum of goats and cows then subtract the overall total so 3 then there are 3 cows in all