This word problem first needs to be turned into equations to help you solve.
First, let's labele what we know.
Each family used a certain amount of water, so lets call the total time water used by the Carter family C and the total time water was used by the Woody family W. Since the total number oh hours that water was used for both families is given in the problem, we can make one equation: C+W =50 hr.
Next, we know the rate that each family used water, so multiplying a rate by a time will give us an amount of water usage in liters for each family. Since the Carters used 35 L per hour and the Woodys use 40 L per hour and total usage is 1900 L, our equation for total water usage is 35 L/hour *C + 40 L/ hour * W =1900 L.
Now that we have two equations and two unknowns, we can solve. The first equation becomes C= 50 hr.-W or W=50 hr.-C, we can use either variation of the equation to substitute into the second equation.
For this example, I will use the form W=50 hr.-C. Plugging this into the second original equation, we get:
(35 L/hr)*(C) + (40 L/hr)(50 hr. -C)= 1900 L
(35 L/hr)*(C) + (2000 L - 40L/ hr. *C)= 1900 L
Grouping like terms, we get:
2000 L+ (35 -40) L/hr *C = 1900 L
Solving for C,
5L/hr * C = 100 L
C= 20 Hours
Plugging this into C + W=50 hours, we can solve for the amount of water used by the Woody family.
20+W= 50 hours