Answer:
frogs = 13
Explanation:
Lets denote
Turtle as t
Frog as f
Crayfish as c
Two hours has nothing to do with the answer, it is added just to confuse the student.
He counted four more frogs than turtles
t = 4 + f ----------- ( 1 )
Number of crayfish was three more than twice the number of turtles
c = 3 + 2 ( t ) ----- ( 2 )
Total, he counted 54 turtles and crayfish
t + c = 54 --------- ( 3 )
How many forgs
f = ?
From eq ( 3 )
c = 54 - t ----- ( 4 )
put c in eq ( 2 )
54 - t = 3 + 2 ( t )
54 - 3 = 2 ( t ) + t
51 = 3 ( t )
t = 17 -------- ( 5 )
put t in eq ( 1 )
17 = 4 + f
f = 17 - 4
f = 13 -----------( 6 )
For finding c put t = 17 in eq ( 4 )
c = 54 - 17
c = 37
To check if the answer is right, put values of t and c in eq 3
17 + 37 = 54
54 = 54 ----- L.H.S = R.H.S