Carla and Rob left a 20% tip at a restaurant. The tip was $6. Carla's lunch cost $15. Write and solve an equation to find the cost of rob's lunch.

Question

I dont know how to find the equation for Rob's lunch cost. 

Answer 1

Hi Kelly!

 

To solve this question, you have to work backwards, stating that Carla's lunch is = C, and Rob's is = R

 

We know that $6 is the value of Carla's tip and Rob's tip put together

We also know that the tip value (V) is equivalent to 20% of their  meal cost, so V = 6 =  0.2 * (R+C) = 0.2 * (R + 15)

Now we break up this equation into V = 6 = (0.2 * R) + (0.2 * 15) = (0.2 * R) + (3), therefore, 6 - 3 = (0.2 * R)

We only have one variable left, so we can solve the equation! 3 = 0.2 * R, R = 3/0.2 = 15