3
algebraJohn is 3 times as old as Mary. In 5 years, he will be twice as old as she is. How old is Mary now?
A
5
B
10
C
15
D
3
Correct Answer: A
Choice Ahoice D is the correct answer.
- Define: Mary = , John = .
- In 5 years: Mary = , John = .
- Equation:
- Solve:
- Verify: Mary 5, John 15. In 5 years: Mary 10, John 20. ✓
Choice Ahoice C is incorrect because this is John's age.
Choice Ahoice B is incorrect because calculation error.
Choice Ahoice D is incorrect because calculation error.