Rate Conversions 13
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>>This is YourMathGal, Julie Harland. Please visit my website at yourmathgal.com, where all of my videos are organized by topic. All right, we’re going to do another example like we did in Example 12. Gas cost 4 dollars and 35 cents per gallon and your car gets 22 miles to the gallon. How much does it cost to drive your car one mile? And let’s round our answer to the nearest cent if we’re going to have to round. Okay. So what we know is that gas costs $4.35 a gallon so we could start with that. $4.35 is what it cost for one gallon, and your car gets 22 miles to one gallon. So one gallon– for one gallon, you get to go 22 miles. So this is telling you, you go– do you pay 4 dollars and 35 cents to go 22 miles? So the question is how much does it cost to go one mile? Gallons cancel, right? So, what we’ve got is basically this $4.35 divided by 22, right, per mile. So that’s going to be $4.35 over 22, right? Whatever that is, per one mile, okay? So, then you get out your calculator. We’re going to do $4.35 divided by 22 and we’re going to round to the nearest cent. So it’s going to be approximately, I’ve got 20 cents per mile. Now, you might have written that as 0.20 per mile. Okay? So either way, we got it. Now if ask you, how much does it cost to drive 10 miles? Of course, you would multiply that by 10, right? It will cost 2 dollars, how much of it, you know, et cetera. So once you know what it is per mile, you can go ahead and multiply it. But I round it here, right? So, let’s just add on to this and change the question slightly. All right, so we’ll just change a little bit. So, gas cost $4.35 a gallon. So again, we got our $4.35 for one gallon. You would start exactly the same. And then we know it’s 22 miles to a gallon. So for one gallon, you go 22 miles. But the question now is, how much does it cost to drive your car 160 miles? So then we just want our final answer to be in many so we could say, “All right, I want to go 160 miles.” Okay? So, look what happens here. The miles cancel, the gallons cancel. And your answer will be in terms of many. So then we just do $4.35 times 160. And we divide by 22 and to the nearest cent, I get 31 dollars and 64 cents. Now, let’s see how about [inaudible] when we round it. When we rounded, we got 20– let’s say let’s go back up. We got 20 cents a mile, right? 20 cents a mile. So, just note, 20 cents a mile, where 160 miles if you did that calculation, what would you get? So you do 160 times 0.2 and it comes to 32 dollars. So when you rounded it, it looks like it cost more, right, but not much more. So $31.64 is really what it cost but had you rounded it to 20 and then multiplied by 160, just note you will get a little bit different answer. This is YourMathGal, Julie Harland. Please visit my website at yourmathgal.com, where all of my videos are organized by topic.

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