Jodi is 13 years old. she is 3 years older than twice her sister Trudi's age. How old is Trudi?

Question

Introduction to Picture algebra

Answer 1

Stephanie,

 

Let T = Trudi's age.  Then Jodi is twice Trudi's age (2·T) + an additional 3 years (2·T + 3).

 

So:  

 

2·T + 3 = 13

 

Subtract 3 from both sides:

 

2·T = 10 

 

Then divide both sides by 2

 

T = 5

 

Trudi is 5 years old.