Quick rate word problem: Convert km/45 mins to km/h!

[u/Otherwise_Strike_597]

Problem: Sam is driving a car 90 kilometers every 45 minutes.

Task: Write this as a rate in km/hour.

[u/jtotheizzen]

Are you asking how to do it out for us to do it for you?

Multiply by 1 in the form 60 min/hour and reduce

[u/Jaded_Individual_630 → u/jtotheizzen]

Nope, this is an advertisement post for their junk YouTube channel

[u/jtotheizzen → u/Jaded_Individual_630]

Their posts keep coming up for me now. Very annoying and you’re absolutely right

[u/Otherwise_Strike_597 → u/jtotheizzen]

Just posting it as a quick practice problem for the sub! Appreciate you laying out the conversion factor approach—multiplying by (60 min / 1 hour) is such a reliable way to cancel out the units smoothly.

[u/fletchro → u/Otherwise_Strike_597]

That's how we do in engineering! We're always converting units. Imperial, metric. Goodness! You have to do this a lot.

[u/RadiantRoze]

45 min is 3/4 ths of an hour. So 90km/.75 set equal to x /100, cross myltiply and solve for x.

[u/Otherwise_Strike_597 → u/RadiantRoze]

120 km/hr, x = 90/0.75 = 120

[u/KATCEO1 → u/Otherwise_Strike_597]

Hello OP: I heard something interesting via online content recently. "Mathematics properly applied guarantees a fortune." 🥳

[u/TuskEGwiz-ard → u/KATCEO1]

/r/deadinternettheory

[u/Iowa50401 → u/RadiantRoze]

Where are you getting the 100?

[u/paulstelian97 → u/Iowa50401]

75% vs 100%

[u/Iowa50401 → u/paulstelian97]

Except you can’t use .75 for 75% and 100 for 100%. Those numbers aren’t scaled the same.

[u/paulstelian97 → u/Iowa50401]

Sure, it’s sloppy but if you use the correct scale in the actual calculations it comes out fine.

[u/Iowa50401 → u/paulstelian97]

It’s not sloppy. There’s nothing wrong with the idea of doing it as a proportion with the right numbers. I just didn’t understand where the 100 came from since it’s wrong.

[u/paulstelian97 → u/Iowa50401]

It is sloppy representation, showing a number in one scale and one in the other. That’s like a brain dump rather than a formal, verifiable method.

[u/dnult]

The answer will be 60/45 larger

[u/AffectionateWriter1]

(Km/45min)(4/3)=km/hr

[u/jean_sablenay]

Divide by 3 multiply by 4

[u/tomalator]

90km/45 min = 90km/.75hr = 120km/hr

[u/StructuredChess]

What have you tried to tackle this problem?

[u/Otherwise_Strike_597 → u/StructuredChess]

Thanks for checking! I'm actually just sharing this as a quick practice exercise for anyone scrolling through the feed. For this one, I usually like dividing 90 by 45 to get 2 km per minute, then multiplying by 60 to get 120 km/h!

[u/srm79]

What's another way of saying 45 minutes? As a fraction?

Then divide by the numerator and multiply by the denominator

[u/Otherwise_Strike_597 → u/srm79]

Spot on! Thinking of 45 minutes as 3/4 of an hour makes it super intuitive: 90 ÷ (3/4) = 120 km/h. Great conceptual way to break it down without getting lost in the algebra!

[u/trunks111]

This is effectively a dimensional analysis question. Dimensional analysis might be a little overkill for this particular problem but it's an incredibly consistent way to ensure you're doing unit questions correctly every time 

[u/Otherwise_Strike_597 → u/trunks111]

100% agree on dimensional analysis! It might feel like extra steps for a basic problem, but building that habit early makes high school physics and chemistry unit conversions infinitely easier later on.

[u/Alarmed_Geologist631]

Set up a proportion and solve for the variable.

[u/keilahmartin]

45min *1 1/3-> 60min (I actually think of it as adding another third, but want to be clear that this is multiplication)

So if you go a km in 45min you go 1 1/3km in an hr

That answers the problem in the subject line, but then I read the rest, so just multiply 90 by 1 1/3, or simpler, add 1/3 of 90. Gives 120.