Question

Michael has $10 to put in a savings account . He has two options for a saving account : Option 1 will add $ 100 to his account each week . - Option 2 will double the amount in his account at the end of each week . a) Write a function in terms of x to model each option of savings . b) Michael wants to have at least $700 in his account at the end of 7 weeks to buy a mountain bike. Determine which option (s) will enable him to reach his goal. Justify your answer.

Answer 1

Option 1:

He starts with $10, and for each week, we add $100

Then his balance as a function of weeks will be:

f(w) = $10 + $100*w

option 2.

Again, we start with $10, and for each week that passes this is doubled, then the equation will be:

g(w) = $10*(2)^w

Now, we want in week w = 7 to have at least $700, then we need to replace w by 7 in both equations and see which one is better.

option 1:

f(7) = $10 + $100*7 = $710

With option 1 he will have enough

option 2:

g(7) = $10*(2)^7 = $1280

Again, he will have more than $700 in week 7, and we can clearly see that this option is better.