# Thread: pls help me w simultaneous equation

1. ## pls help me w simultaneous equation

1. Last year, Andy invested $5000 in company X,$4000 in company Y and $3000 in company Z. He made a profit of$850 for the year.

During the same time period, Bryan invested $4500 in company X,$900 in company Y and $3600 in company Z. He made a profit of$657 for the year.

Similarly, Charles invested $4000 in company X,$2400 in company Y and $1600 in company Z. He made a profit of$552 for the year.

If Mary invested $2800 in company X, how much profit will she make for the year? 2. Originally Posted by dorwei92 1. Last year, Andy invested$5000 in company X, $4000 in company Y and$3000 in company Z. He made a profit of $850 for the year. During the same time period, Bryan invested$4500 in company X, $900 in company Y and$3600 in company Z. He made a profit of $657 for the year. Similarly, Charles invested$4000 in company X, $2400 in company Y and$1600 in company Z. He made a profit of $552 for the year. If Mary invested$2800 in company X, how much profit will she make for the year?
let
$\displaystyle x_p$ denoted for the profit from X
$\displaystyle y_p$ denoted for the profit from Y
$\displaystyle z_p$ denoted for the profit from Z

so

$\displaystyle 5000x_p+4000y_p+3000z_p=850.....Andy$

$\displaystyle 4500x_p+900y_p+3600z_p=657.....Bryan$

$\displaystyle 4000x_p+2400y_p+1600z_p=552.....Charles$

then solve these equation to find $\displaystyle x_p$ then the number you have present the profit from X so you have just to multiply it with how many mary invested in it ...that's all

3. i tried for a long time still doesn't know how to get the answer.
could u tell me am i suppose to use substition or elimination to solve this question?

4. Originally Posted by Amer
let
$\displaystyle x_p$ denoted for the profit from X
$\displaystyle y_p$ denoted for the profit from Y
$\displaystyle z_p$ denoted for the profit from Z

so

$\displaystyle 5000x_p+4000y_p+3000z_p=850.....Andy$

$\displaystyle 4500x_p+900y_p+3600z_p=657.....Bryan$

$\displaystyle 4000x_p+2400y_p+1600z_p=552.....Charles$

then solve these equation to find $\displaystyle x_p$ then the number you have present the profit from X so you have just to multiply it with how many mary invested in it ...that's all
I divide the first one by 1000 and the second by 300 and the third by 400

$\displaystyle 5x_p+4y_p+3z_p=.85.....Andy$

$\displaystyle 15x_p+3y_p+13z_p=2.19.....Bryan$

$\displaystyle 10x_p+6y_p+4z_p=1.38.....Charles$

now it is easy to solve multiply the first by -3 and add it to the second
you have an equation with two variable then multiply the first one with -2 and add it yo the third you will get two equation just with y,z solve them .

best wishes