What’s the difference between “to reduce ʙʏ one-third” and “to reduce ɪɴᴛᴏ one-third”?
A sample of fluorine gas occupies a volume of 600 mL at 760 torr. Given that the temperature remains the same, calculate the pressure required to reduce its volume by one-third.
I don't need an answer. I just want to know what operation the question is referring to.
What confuses me is the part at the end of the question: does reduce its volume by one-third refer to reducing the volume by one-third? Like you subtract one-third of 600 into 600?
Or does it refer to reducing the volume of 600 into one-third meaning that 600 should be divided by three?
by is a very versatile preposition. Most comments so far could easily have been made into answers, so I claim no greater authority in setting out this understanding:
by: Preposition
If something increases or decreases by a particular amount, that amount is gained or lost.
"Violent crime has increased by 10 percent since last year."
"Their pay has been cut by one-third."
Collins dictionary
A reduction by one third is a decrease of one third: so 600 ml is to be decreased by 600/3 ml (= 200 ml) to a final volume of 400 ml.
As commented by others, a reduction into one third would be a reduction to 600/3 ml (= 200 ml).
I draw your attention to the careful exclusion of ambiguity by the formulation of the question. The volume is expressed in units of ml. The reduction is expressed only as a number (1/3); it has no units. There is therefore no reason to interpret the question as meaning a reduction of 600 ml by 1/3 ml to 599.666... ml. Nor may we imagine that the 600 ml is to be compressed to 1/3 ml.