Ratio of A to B

[joonkimdds]

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when a question says
"what's the ratio between A to B"

isn't this always have to be in A/B form?

I found that 1 dollar is 21/5 quilos
and the questions asks me to find the ratio between dollar to quilos
so I set it as 1/ (21/5)
and thus the answer should be 5/21 in my opinion,
but the correct answer was 21/5.
5/21 was also one of the answer choices.

 

[UCB05]

when a question says
"what's the ratio between A to B"

isn't this always have to be in A/B form?

I found that 1 dollar is 21/5 quilos
and the questions asks me to find the ratio between dollar to quilos
so I set it as 1/ (21/5)
and thus the answer should be 5/21 in my opinion,
but the correct answer was 21/5.
5/21 was also one of the answer choices.

As you had set up: 1 dollar = 21/5 quilos>>> rearranged, yes you can move units>>> dollar/quilos (your A/B)= (21/5)/1 = 21/5

 

[joonkimdds]

As you had set up: 1 dollar = 21/5 quilos>>> rearranged, yes you can move units>>>
dollar/quilos (your A/B)= (21/5)/1 = 21/5

1 dollar is 21/5 so if you write (21/5)/1 that means it's quilos/dollar not dollar/quilos.

 

[UCB05]

1 dollar is 21/5 so if you write (21/5)/1 that means it's quilos/dollar not dollar/quilos.

1 dollar = 21/5 quilos
Move quilos to the left by dividing both sides with quilos:
1 dollar/quilos = 21/5

 

[joonkimdds]

hm... so is it wrong to say A to B is A/B while B to A is B/A?

This seems like the only exception to the rule.

For example, ratio of areas of the new(35) to the old(18) = new/old = 35/18 is the answer instead of 18/35.

What makes the dollar to quilos example different from above?

 

[UCB05]

hm... so is it wrong to say A to B is A/B while B to A is B/A?

This seems like the only exception to the rule.

For example, ratio of areas of the new(35) to the old(18) = new/old = 35/18 is the answer instead of 18/35.

What makes the dollar to quilos example different from above?

If you just think of it in terms of what the question asks, it wants you to convert dollars to quilos. Which means the answer you want is quilos in the numerator.