Fred brown and his sister, Nancy, each have $15 in the bank. Every week Nancy plans to add $3 to her account. Fred who loves to spend money when he has it, plans to add $1 to his account each week. How many weeks will it take Nancy's account to have TWICE as much money as Fred's account?

(Explain your thinking)

it will take 15 weeks for Nancy's account to have TWICE as much money as Fred's account

Step-by-step explanation:

Fred brown and his sister, Nancy, each have $15 in the bank

Initially both Fred and Nancy have $15

Every week Nancy plans to add $3 to her account

Let 'n' be the number of weeks she plans to add in her account

for 1 week, $3

For n weeks, its 3n

So amount of money in Nancy's account after 'n' weeks = 15 + 3n

Fret plans to add $1 to his account each week

for 1 week, $1

For n weeks, its 1n

So amount of money in Fred's account after 'n' weeks = 15 + 1n

Now we need to find out 'n' when

Nancy's account = 2 times of Fred's account

15 + 3n = 2 (15+1n)

Distribute 2 inside the parenthesis

15 + 3n = 30 + 2n

Subtract 2n on both sides

15 + n = 30

Subtract 15 on both sides

n = 15

Hence, it will take 15 weeks for Nancy's account to have TWICE as much money as Fred's account