Question 1203059
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Suppose you want to have $400,000 for retirement in 20 years. Your account earns 7% interest. 

a) How much would you need to deposit in the account each month?

b) How much interest will you earn?
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The problem's formulation in the post is presented monstrously flippantly: 
period of compounding is not given and the term "compounding" itself 
even is not mentioned.


When I see a problem presented so  {{{highlight(highlight(inaccurately))}}} / {{{highlight(highlight(carelessly))}}},  I prefer do not touch it.


For future generation of students, who will see this post, I only want to point 
that the total payment calculation in the post by @Theo is incorrect.