You begin with $25 in a savings account and $50 in the checking account. each week you deposit $5 into savings and $10 into checking. after how many weeks is the amount in checking twice the amount in savings? write and solve an equation.

Let  represent the amount is saving account after n weeks, and  

let  represent the amount is checking account after n weeks.

so:



and 



thus to find

"the amount in checking twice the amount in savings"
 
we solve the equation:

50+10x=2(25+5x),

50+10x=50+10x

this is true for any x (any number of weeks)

the amount in checking is twice the amount in savings ALWAYS