Ryan was 8 when his parents invested $4000 in a certificate of deposit that pays 6%. If Ryan leaves the account alone until the investment doubles, how old will he be? (Assume that the interest is not compounded.)
<span>This one has a twist to it in that it tells you that the interest is not compounded. </span>
<span>They need to earn $8,000 - $4,000 = $4,000 in interest. </span>
<span>They earn $4,000 X 6% = $240 in interest per year. </span>
<span>$4,000 / $240 = 16.67 </span>
<span>16.67 + 8 = 24.67 </span>
<span>Ryan will be 24 and 8 months old when the investment doubles. </span>
<span>2.)Benjamin has $6000 invested in two accounts. One earns 8% interest per year, and the other pays 7.5% interest per year. If his total interest for the year is $472.50, how much is invested at 8%? </span>
<span>X = the amount invested at 8% </span> <span>($6,000 - X) = the amount invested at 7.5% </span>
<span>So: </span>
<span>.08X + .075(6,000 - X) = $472.50 </span>
<span>Now solve: </span>
<span>.08X + 450 -.075X = $472.50, this reduces to </span> <span>.005X = $22.50, which finally reduces to </span> <span>X = $4,500 </span> <span>So $6,000 - X = $1,500 </span>
<span>So the answer is: $4,500 is invested at 8% </span>
<span>Test the result </span>
<span>$4,500 X 8% = $360.00 </span> <span>$1,500 X 7.5% = $112.50 </span>
<span>$360.00 + $112.50 = $472.50, and you've proved your answer</span>
If you meant " | ", as in |x|, that's "absolute value." The domain of this function is "all real numbers," and the range is "all real numbers zero or greater."