Solve each system of equations by writing a new system that eliminates one of the variables.
2x+y=25
4x+3y=9

Step-by-step explanation:

Let:

We need to eliminate one of the variables, so let's use elimination method. First multiply (1) by 2

Now subtract (2) from 2*(1) in order to eliminate x:

Solving for y:

Multiplying both sides by -1  

Finally, replacing the value of y in (1)

Solving for x:

add 41 to both sides:

Multiply both sides by 1/2:

step-by-step explanation:

the original amount doesn't ''re just looking for the time it takes for 1/2 of the substance to we have

(1/2) =)     take the ln   of both sides

ln (1/2)   = )   and we can write

ln(1/2) = ) lne     and lne   = 1     so we have

ln(1/2) = -.1092t     divide both sides by -.1092

t = ln(1/2)/-.1092 = about 6.347 days = about 6.3 days (rounded)