Answer
19
Step-by-step explanation:
For this example, R = Richard and L = Lilia. You'll need to set up a system of equations with the information that the problem gives you.
R = L + 7
(R+10) + (L+10) = 51
Use the substitution method so that you only have one variable in the equation. The first equation tells you that R is the same as L+7, so put L+7 instead of R everywhere you see R in the second equation.
[(L+7) + 10) + (L+10) = 51
L + 7 + 10 + L + 10 = 51
Combine like terms.
2L + 27 = 51
Isolate the variable by subtracting first, then dividing.
2L + 27 - 27 = 51 - 27
2L = 24
2L/2 = 24/2
L = 12
You just solved for L (Lilia's age). Don't forget that you're trying to find R (Richard's age), so plug your L number into the first equation.
R = L + 7
R = 12 + 7
R = 19
Check your answer by plugging your solutions (R and L) into the second equation and see if it's true.
(R+10) + (L+10) = 51
(19+10) + (12+10) = 51
29 + 22 = 51
51 = 51 is true.
