(25000-f)(.03)+.05f=1100
750-.03f+.05f=1100
750+.02f=1100
.02f=350
f=$17500
So Mary invested $17500 @ 5% and 7500 at 3% to earn $1100 in interest.
20x+ 5y = 15
Move 20x to the other side. Sign changes from +20x to -20x
20x-20x+5y=-20x+15
5y=-20x+15
Divide both sides by 5
5y/5=y ( Cross out 5 and 5, divide by 5, 1*1*y=y)
-20/5=-4x
15/5=3
y=-4x+3 or y=3-4x
Answer: y=-4x+3 or y=3-4x
28:35
Those are divisible by 7 so divide both sides by seven
the answer is 4:5
