Jack should invest $8400 in the CD account and $3600 in the savings account.
Step-by-step explanation:
Jack wants to earn 7.5% interest per year. That implies he wants to earn
7.5/100*12000 per year i.e $900 per year.
Lets assume he invests X amount in the savings account. That leaves 12000-X to be invested in the CD account.
That implies,
[tex]4/100*X + 9/100*(12000-X) = 900[/tex]
=> [tex](4X+108000-9X)/100 = 900[/tex]
=> [tex]-5X = 90000-1080000 = -18000[/tex]
=> X = 3600
