Standard to metric conversion calculations.
Those calculations were useless then, and we knew it-- we were saying to one another “Why don’t they just teach us metrics?” They are even more useless now, and if the US actually used metrics, they would be something even more useless than plain uselessness.
We had to solve pages of problems like “5 1/2 feet = _____ meters?”
Since we had not learned decimals, we had to calculate by dividing dividing 5 1/2 by 3 1/4, with pencil and paper (show your work!) And the conversion formulae were supposed to be committed to memory.
The above is my answer to the OP. If that’s all you are interested in, go on to the next post; but for the interested, what follows is a bit of an OP/ED (READ: Rant, albeit, informative, well-punctuated, and with paragraph breaks) about WHY the US failed so miserably to convert to the metric system back in the 1970s.
In the third grade, our teachers announced the US conversion to metrics. In addion to regular math, we were going to have a unit on metrics every day (extra math? 
) The “metrics unit” meant memorizing a lot of formulae, and doing endless problems that involved converting “8 liters to gallons”; “7 feet to meters”; and the dreaded “15 grams plus two pounds = how many kilograms?” and so forth. We had not learned decimal places yet, although we had learned rounding up and down, so the problem would ask us either to “round up, or truncate.” And every problem involved a fraction.
If would have been far easier had they simply taught us decimals first, but out curricula said decimals were a 6th grade skill. Nevermind that metrics is a decimal system.
At some point, we further learned to calculate the centimeters remaining on something like feet to meters problems, or the inches left on a problem going the other way. I don’t think we learned to calculate the ounces left on a liter to pound calculation/deciliters, centiliters, whatever, or lower measures on anything other than measures of length, although we did learn the prefixes: deci, centi, mili, micro/deca, hecto, kilo, mega-- I think that’s the number of places we learned, and that “centi” and “kilo” were the key ones to remember, and why.
Oh, dear lord was this boring. And it taught us nothing about metrics, other than that it was hopelessly long and complicated-- when the opposite was true.
This was 1975-76, right after Pres. Ford had signed The Metric Conversion Act, and the US was supposed to convert to the metric system, like the rest of the world. It notes that in 1975, The US was in the company Liberia, Yemen, Brunei, and Burma in not having converted to the metric system. Currently, the other four are using the metric system, and the US is having a party to which no one has come,
I firmly believe that, if all children across the US were being taught conversions as I was, that was the exact reason the conversion failed.
Instead of being taught to “think in metrics,” we were being taught that the metric system involved a lot of hard math, and took a long time.
Remember, this happened about that same year that IBM made “pocket” (not really, they were about they size of three large smart phones, stacked) calculators affordable to the middle class, by pricing them at around $30 (about $180 buying power in 2026) instead of the $300 (about $1800 buying power in 2026) they’d been since they’d come on the market around 1971. No one envisioned us performing these calculations quickly with a Smart phone app-- not that we would have needed to, had conversion succeeded.
There was a method to the madness, but it was not well-thought out: it was that all this converting would train us to do quick estimates in our heads of what n liters equaled in gallons (etc.)
This “quick estimate” method was maybe a good way of teaching adults over about 30 to deal with metrics, and adults, mostly over 30, conceived it. Children, however, were not “firmly set,” in the standard system. Children (and willing adults), should probably have moved away from standard together, and learned metrics from the ground up.
In other words, for about 1st - 6th grade (in pre-K, simply “speak metric”), have a lot of class activities where kids took turns measuring things with metric instruments-- metric scales (they could even weigh themselves), metric rulers-- measuring things around the classroom, etc. Kids would be clamoring to have their turn.
Worksheets would have questions like “How would you measure weight? A) in grams; B) in meters; or C) in liters”
And
"(Fill in the blank) “A cat is measured in _________________?” The answer sought would be kilograms, but if many students wrote “centigrams,” this could provoke a class discussion.
As the class learned to conceptualize metrics, worksheets would progress to questions like "A cat weighs about ___________________. (Anything from 3 - 5 grams would be acceptable.)
And, of course, “2 liters of water weighs ______________.” And “Water freezes at _______________ degrees _____________.”
Those questions are kiloliters, kilometers, and kilograms easier than conversion calculations, and as far as schoolwork goes, “fun.” They ask for educated opinions in some cases, and kids like those kinds of questions. The “2 liters of water equals 2 kilograms of water” is a gimme for kids half-paying attention, and throwing a few of those in a quiz or worksheet is a good idea-- it momentarily relieves stress, and is like comic relief in a drama.
I would have looked forward during the school day to metrics had it been taught like that. I would have used it all the time, and tried to get my parents to use it (being academics who spent a lot of time in Europe, they surely would have). I think this is generally true; at the time, this was not a partisan issue-- it was something with a lot of popular support.
The divisions were somewhat along class lines, even more along generational ones (and the Standard supporters would die off first). The class lines blurred as well, because academics, and anyone in a STEM field preferred it-- but so did lots of people who were mechanics and plumbers, and in other skilled labor fields, because parts and equipment frequently came in metrics. The same for anyone with a military background-- the US military had converted to metrics in 1957. Nonskilled labor, to the extent that these were people who came from other countries actually had to learn Standard to function here, after having grown up with metrics.
I think the US pulled the rug out from under itself here. For several years, I hated the metric system; I learned to appreciate it, and use it, only in my late 20s. It’s all I use now, unless I’m speaking to someone who doesn’t know it, or talking about the outside temperate to Americans (even STEM people us Fahrenheit to discuss the weather here. Eh. The Brits still weigh themselves in stones.)
Now, I’m a little angry about this failure; I don’t know why it happened-- why this method of teaching was chosen (big donation from IBM?) But it was my generation’s loss.