# Part 2 – More Revision and Practice, changing the subject of an equation

These examples are a bit more difficult that in my previous post.

• M=2P  (Who is older, Mo or Polly?)

The easiest way of working this out is to give P an imaginary age, and work out Mo’s age. The equations says Mo is double Polly, so if Polly is 20, Mo would be 40. So Mo is older.

• M = 2P (What is Polly’s view of the relationship, in other words, write P=…..)

Try these….

1. X=2Y. What is Y’s point of view?
2. C=Y+12.What is Y’s point of view?
3. D=2Y-1.What is Y’s point of view?

To check your answers, give the person on the right hand side of the equation an age, work out the age of the “subject” person, and then work backwards in your answer to check you get back to where you started.

Here are some more:

1. X=2Y+4. What is Y’s point of view? If Y is 20, how old is X?
2. C=3Y+2.What is Y’s point of view? Again, pretend Y is 20.
3. D=2Y-5.What is Y’s point of view?
4. A=2Y-6.What is Y’s point of view?

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