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=…..)

The answer is P=M/2

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?

Points of view (changing the subject of an equation)

This post is practicing simple equations. In 3 days there will be another one to change the subject of more simple equations. If you write your answers in the box at the bottom I will check them and reply to you. I won’t publish them on the page though!

• “I am forty-one years older than you” is my point of view. In algebra language I would write R=C+41
• What’s your point of view?
• C=R-41

Looking at some of the people in my family then,

• R=D+26 (I am 26 years older than D, my oldest daughter)
• What’s her point of view?
• D=R-26

Now let’s look at another relationship in my family,

• R=G+28
• Who is older? R or G?
• R is older than G, by 28 years.
• so how would G see it?
• G=R-28

Now here’s something you can work out,  given I am 54 at the moment,

1. How old is C?
2. How old is D?
3. How old is G?
4. One more person in my family is T. R=T (that’s my point of view) How old is T?
5. What is T’s point of view, in other words write T=…