Teacher cannot tell what I am doing?

Question

Solve by any method: 0.1x + 0.06y = 9 and 0.09x + 0.5y = 52.7 Check your solution.

My answer:
0.1x=9-0.06y
x= 9-0.06y/ 0.1 = 90 – 0.6y

0.09(90 – 0,6y) _ 0.5y = 52.7
8.1 – 0.054y + 0.5y = 52.7
0.456y = 52.7 – 8.1
y= 52.7 – 8.1/ 0.456 = 97.807

x= 90 – 0.6 * 97.807 = 31.3158
(31.3158, 97.807)

Check:
0.1* 31.3158 + 0.06 * 97.807 = 9
0.09 * 31.3158 + 0.5 * 97.807 = 52.7

Teacher: Sorry, . I cannot tell what you are doing. 0 points
ok.. was the question asked wrong?

Answer 1

its because you stuffed up!

0.1x + 0.06y = 9
0.09x + 0.5y = 52.7

0.1x = 9 - 0.06 y
x = (9-0.06y)/0.1
x = 90-0.6y

Right so far.

Substituting in equation 2

0.9 (90-0.6Y) + 0.5 y = 52.7
8.1 - 0.054y + 0.5 y = 52.7
0.446y = 44.6 You went wrong here. You wrote 456y.
y = 100

substituting back into equation 1

0.1x + 0.06*100 = 9
0.1x + 6 = 9
0.1x = 3
x = 30

Answer 2

The problem your teacher has is that he/she doesn't really understand algebra. Except for the addition error you make on line 6, your work looks good.

You probably should say in your notations:
"Solve for X in terms of Y"
0.1x=9-0.06y
x= 9-0.06y/ 0.1 = 90 – 0.6y
X = (90-0.6y)

Then add the note :

"Substitute X in terms of Y"
0.09x + 0.5y = 52.7
"Since X = (90-0.6y)"

0.09(90 – 0,6y) + 0.5y = 52.7

and continue. The math error that caused you to get the wrong answer would be immediately obvious.

Your methodology is sound, but this teacher needs help understanding the "steps" you left out....

Answer 3

...0.054y + 0.5y = 0.446y NOT 0.456y

so... y = 100 and x =30

solve for x (part 1)
0.1x + 0.06y = 9
0.1x = 9 - 0.06y
x = ( 9 - 0.06y ) / 0.1
x = 90 - 0.6y

solve for y
0.09x + 0.5y = 52.7
0.09 (90 - 0.6y) + 0.5y = 52.7
8.1 - 0.054y + 0.5y = 52.7
-0.054 y + 0.5y = 52.7 - 8.1
0.446y = 44.6
y = 44.6 / .0446
y = 100

solve for x (part 2)
x = 90 - 0.6y
x = 90 - 0.6 (100)
x = 90 - 60
x = 30

Answer 4

First correct answer is given by Chris. Your teacher was probably just too lazy to check your work. When you performed your 'check', it seemed correct because the number .446 is pretty close to .456 which you used instead.

Your reasoning is sound. You made two mistakes:

1) You used a minus instead of a plus but corrected it in the following line so this does not count.
2) You made an arithmetical error by using .456 instead of .446.

I think you may have been tired and your eyes were squinting a little or playing tricks on you!

Answer 5

0.1x + 0.06y = 9
0.09x + 0.5y = 52.7

0.1x=9-0.06y
x= 9-0.06y/ 0.1

0.09((9-0.06y)/0.1)+0.5y=52.7
0.81-0.005y+0.050y=5.270
0.81+0.045y=5.270
y=99.111

x= (9-0.06*99.111)/0.1
x=30.503

check:
0.1*30.530+0.06*99.111=9
9=9

0.09*30.530+0.5*99.111=52.7
52.7=52.7

Answer 6

At least in this mail you made some typos... the first one is:
x= 9-0.06y/ 0.1 = 90 – 0.6y
it should be:
x= (9-0.06y)/ 0.1 = 90 – 0.6y

It would be good if you asked your teacher. Do it again and present it to him or her without typos :).

Answer 7

You are making too much calculations , each calculation can introduce an error. When looking at all the numbers you write down I get pain in the stomach....
do you trust the answer when you see all those calculations ?

instead of doing it the dumb brute force way , I would multiply first equaltion with 90, and the second one with 100

this will give you much more transparent calculations

Answer 8

Ramadan unquestionably has not something to do with instructors telling their pupils to end their food. it extremely is a non secular undertaking and is declared with the help of people who persist with. toddlers, those with particular regulations/obstacles and the elderly are common

Answer 9

you made a small arithmetic mistake, which the teacher should have easily seen. Your reasoning was sound, and appropriate.

You should speak to her and see if she will reconsider the grade, as it looks right to me

Answer 10

To be honest, it looks like you need a tutor.