Question 1123392
The system of equations:
1. A financial planner put some of it into a savings account paying 4% annual simple interest. The rest was invested in a riskier mini-mall development plan paying 13% annual simple interest. The combined interest earned for the first year was $638.

{{{.04*X+.13*Y=638}}}

2. investing $6,950 of a couple's money 

{{{X+Y=6950}}}

System:
{{{.04*X+.13*Y=638}}}
{{{X+Y=6950}}}

Rewrite and Plug-In

{{{.04*X+.13*Y=638}}} && {{{X=6950-Y}}}
{{{.04(6950-Y)+.13*Y=638}}}
{{{278-0.04*Y+0.13*Y=638}}}
{{{-0.04*Y+0.13*Y=360}}}
{{{0.09*Y=360}}}
{{{Y=360/0.09}}}
{{{Y=4000}}}

{{{X=6950-Y}}}
{{{X=6950-4000}}}
{{{X=2950}}}

$4000 was invested in the risky mini-mall dev plan, while $2950 was invested in the savings account.