Question

Susan Marciano invested part of her 28,000 bonus in a fund that paid an 11% profit and invested the rest in stock that suffered a 5% loss. Find the amount of each investment if her overall profit was 2,920

Answer 1

a = amount that paid 11% profits

b = amount that lost 5% profits

we know that whatever those values are, a + b = 28000.

how much is 11% of "a"? well, (11/100) * a = 0.11a.

how much is 5% of "b"? well (5/100) * b = 0.05b.

$a+b=28000\implies b=28000 - a \\\\[-0.35em] ~\dotfill\\\\ \stackrel{paid~11\%}{0.11a}~~ \stackrel{\stackrel{loss}{\downarrow }}{-} ~~\stackrel{lost~5\%}{0.05b}~~ = ~~\stackrel{overall~paid}{2920} \\\\\\ \stackrel{\textit{substituting on the 2nd equation}}{0.11a~~ - ~~0.05(28000-a)}=2920\implies 0.11a+0.05a-1400=2920 \\\\\\ 0.16a-1400=2920\implies 0.16a=4320\implies a=\cfrac{4320}{0.16} \\\\\\ \boxed{a=27000}~\hspace{10em}\boxed{\stackrel{28000-a}{b=1000}}$