It takes Andre 4 minutes to swim 5 laps. How many laps per minute is that?
2 answers:
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Let's call Maura's age now M and Cara's age now C.
We know Maura is five years younger than Cara. In symbols that is, M - 5 = C
We also know that 7 years ago Maura's age was half of Cara's. Maura's age 7 years ago was M-7 and Cara's age seven years ago was C-7. Since Maura's age (7 years ago) was half of Cara's we can write in symbols:
Let's take that last equation and substitute C - 5 for M (this is because according to our first equation these are equal). When we do this we get an equation with only C as the variable and solve for C as follows:
Cara is 17. Since Maura is 5 years younger she is 12.
As a check, seven years ago Cara was 10 and Maura was 5. It is the case that Maura was half Cara's age seven years ago.
We know Maura is five years younger than Cara. In symbols that is, M - 5 = C
We also know that 7 years ago Maura's age was half of Cara's. Maura's age 7 years ago was M-7 and Cara's age seven years ago was C-7. Since Maura's age (7 years ago) was half of Cara's we can write in symbols:
Let's take that last equation and substitute C - 5 for M (this is because according to our first equation these are equal). When we do this we get an equation with only C as the variable and solve for C as follows:
Cara is 17. Since Maura is 5 years younger she is 12.
As a check, seven years ago Cara was 10 and Maura was 5. It is the case that Maura was half Cara's age seven years ago.