When you can figure out actual # using ratios?

[Ratioman]

Say I am given ratios of 3:5 (white socks : red socks) on a DS. And it asks me the actual number of socks combined. Whar sort of additional facts would I need to figure that out? Of course I can figure it if they tell me the total # of socks...

but what if it said something like if you add 5 blue socks, then the ratio among three would be (just making this up) 2:4:3. Would this be enough?

Or what about, if you double the number of white socks, the combined total would be (again, just making this up) 18.

Is there some kind of a rule that says, when you have ratio and you are trying to figure out the actual number, you need the following: ....


Thank you!

[ratio man 2]

Say I am given ratios of 3:5 (white socks : red socks) on a DS. And it asks me the actual number of socks combined. Whar sort of additional facts would I need to figure that out? Of course I can figure it if they tell me the total # of socks...

but what if it said something like if you add 5 blue socks, then the ratio among three would be (just making this up) 2:4:3. Would this be enough?

Or what about, if you double the number of white socks, the combined total would be (again, just making this up) 18.

Is there some kind of a rule that says, when you have ratio and you are trying to figure out the actual number, you need the following: ....


Thank you!

Not to answer my post, but I have been struggling with this concept and get it wrong all the time.. I've read up on this topic and this is what I am thinking

White: Red is 3:5. That's like saying 3x:5x where x is some sort of a multiplier.

If I double the number of white socks then I am doing [(2)*(3x)]:5x. Now I am saying 6x + 5x = 18 or 11x=18, so x is 18/11. This means that in the beginning I had (3)(18/11) white socks and (5)(18/11) red socks. I know the numbers aren't pretty, but is the logic correct?

Now for the whole blue socks mess:

Can do 3x + 5x + 4 = 2x + 4x + 3x ?

So I'd get 8x + 4 = 9x, which means x = 4.

So originally, I had 12 white socks and 20 red socks? This one doesn't seem right. Maybe it's because I made up numbers and they don't work? Thanks.

[rfernandez]

White: Red is 3:5. That's like saying 3x:5x where x is some sort of a multiplier.

If I double the number of white socks then I am doing [(2)*(3x)]:5x. Now I am saying 6x + 5x = 18 or 11x=18, so x is 18/11. This means that in the beginning I had (3)(18/11) white socks and (5)(18/11) red socks. I know the numbers aren't pretty, but is the logic correct?

Yes, this is correct logic.

Now for the whole blue socks mess:

Can do 3x + 5x + 4 = 2x + 4x + 3x ?

So I'd get 8x + 4 = 9x, which means x = 4.

So originally, I had 12 white socks and 20 red socks? This one doesn't seem right. Maybe it's because I made up numbers and they don't work? Thanks.

Again, the numbers don't work out here, but the reasoning is right. The reason the numbers come out a little screwy is that the 3:5 ratio would have to be preserved between white and red socks even if blue socks are introduced. The 2:4:3 ratio would not be possible.