| Author | someone solve this math question please ? |
|---|
7 times a digit number is equal to 4 times the number obtained by reversing the digits.If the digits differ by 3,find the number.
Please show the working too !
My answer was -36 but the book says 36,so i dont know what went wrong i checked my answer several times.. |
| I know i'm not supposed to post this here , BUT i have to rely on my precious LORDSWM community. |
My answer was -36 but the book says 36,so i dont know what went wrong i checked my answer several times.
Both answers are same |
| Do u mean minus 36? |
Yes i suppose you're right.
Here's my working please check it -
let the ten's digit = x
one's digit = y
7(10x + y ) = 4(10y + x)
70x+7y = 40y + 4x
66x=33y
66x-33y=0
33(2x-y) = 0
2x-y = 0 --------> equation 1
2) X-Y=3 -----> equation2
no ,
subtracting the equations -
y= -6
substituting value of y in umm...umm.. equation 1
2X-(-6)= 0
2X+6 = 0
X= -3
So the number is -36 |
yes i mean minus 36
admins dont delete please. |
It doesn't say which digit is larger, so if you replace equation 2 with y-x=3 you get the answer 36.
Also both solutions are correct since the problem doesn't ask for a positive number. |
| let me try. |
Also both solutions are correct since the problem doesn't ask for a positive number.
doesn't matter if the question doesn't mention that the number is positive. There can be only one answer... |
second equation is abs(X-Y)
so, you need to resolve two systems of equations:
1) 2x-y = 0
x-y = 3
2) 2x-y = 0
y - x = 3
The solution of second system is (X=3;Y=6). I think this is your correct answer=) |
If we do this -
2x-y = 0 minus y-x = 3
2x - y=0
-x + y =3
when we change the signs and compute it we get
3x-2y=-3. |
if we do this
1) 2x-y = 0
x-y = 3
we get X=-3
If we do this
2) 2x-y = 0
y - x = 3
we get x=3,
how do we determine,if X is greater or Y is greater ?
Also when we subtract 2x-y from y-x
we usually change signs right ?
So after rearranging we'll get
2x-y = 0
-x + y= 3
try computing this. |
2) 2x-y = 0
y - x = 3
The solution of second system is (X=3;Y=6). I think this is your correct answer=)
you're right ! Thanks a lot =)
But how do we determine to take x-y or y-x ?
Also
if we check the conditions or -36 and 36 both of them satisfy the conditions of the questions !
7(-36) = 4(-63)
and
7(36) = 4(36) which one is correct answer ? |
Post here :
https://www.lordswm.com/forum_thread.php?id=111 |
I'm only lvl 2 doofus.
And also even if i post it there i won't be able to reply,so please let this topic stay ! =) |
do you know how to resolve system of equations?
you can to add or to subtract an equations! So 2x-y+(y-x) = 3 is equal to x = 3! |
Thanks !
problem solved ! |
| If you can't post in the appropriate thread then don't post at all, as simple as that. And how long will it take you to learn to use a proper title ? |
| closed by CopyNinja (2012-06-22 17:59:56) |
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