Question 168004
Once you call the unknown by a letter, it falls into place, usually
Let {{{x}}}= the amount invested at 7%
Then it gives you
{{{2x + 3000}}}= the amount invested at 10%
Now the problem wants to know how much was made from the 2 investments
Think of this as the profit.
{{{.7x + .1*(2x + 3000) = 3810}}}
{{{.7x + .2x + 300 = 3810}}}
{{{.9x = 3810 - 300}}}
{{{.9x = 3510}}}
{{{x = 3900}}}
This was the amount invested @ 7%
{{{2*3900 + 3000 = 10800}}}
This was the amount invested @ 10%
check:
{{{.7x + .1*(2x + 3000) = 3810}}}
{{{.7*3900 + .1*10800 = 3810}}}
{{{2730 + 1080 = 3810}}}
{{{3810 = 3810}}}
OK
He invested $10,800 @ 10%