Rebecca Wright earned $115 in simple interest for 8 months at an annual interest rate of 5%. A. What formula would you use to find out how much money she invested? B. Set up a formula and solve to find out the amount initially invested.

1 Answer
Tony B
Jan 17, 2018

#$3450#

Identify key points in a question. Determine where you need to go with your solution (target). Ask yourself; how can I use what I have got to get to my target.

Explanation:

Let the principle sum (initial deposit) be #P#

8 months is #8/12# of 1 year

Interest for 1 years is #5/100xxP -> ?#

However, we are told that #$115# is the interest for 8 months so we have:

#8/12xx5/100xxP=$115#

#2/3xx5/100xxP=$115#

#(cancel(10)^1)/cancel(300)^30xxP=$115#

#P=$115xx30 = $3450#

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