1/4 – 5/8 =? Subtract Fractions using these 2 Ways! BASIC MATH!

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[jomerrell]

I love your site. As a 72 year old woman married to a man who uses math all day long in his business but has to carry a pocket of batteries or plug ins to keep his math calculators spinning I'm proud that I can do most of your equations in my head faster than he can punch the numbers into his external battery operated 'brain'. Thanks for making the challenges fun.

[Ayelmar]

Solved in my head at the thumbnail, my answer is -38.
1/4 -5/8 = 2/8 - 5/8 = -3/8
(The lowest Common Denominator between the two fractions is 8, so we get both fractions to the LCD, then subtract.)

[gregpoehlein]

The bow tie method is just a fancy way of saying to multiply both sides by 1. Left side is multiplied by right side denominator over itself (8/8) and the right side by the left side over itself (4/4). Thus you get 8/32 - 20/32 with 32 being a common denominator (not LCD) without having to worry about which cross multiplication to do first.

[russelllomando]

got it -3/8 easy one thanks for the fun

[bigdog]

super simple. First rewrite to addition:
(-5/8) + 1/4

Now this is simple enough that we know 8 is the lcd so we rewrite the problem to:
(-5/8) + (2/8)

- 5 + 2 = -3 so the final answer is negative 3 eighths.

[HR-wdcw]

LCD is 8, so you multiple the top and bottom by 2 to get (2/8) - (5/8) which then equals the negative 3/8.

[quaver]

Did it mentally. Answer is -3/8. And am 82 years old. This is a very easy one that does not need any fancy method.

[clmkc]

Unrelated but look at "Kaprekars Constant" of 6174.

Take a 4 digit number and rearrange the numbers from highest to lowest. Subtract the smaller number from the larger. Within 7 iterations or less, you always come back to 6174. Not sure why!

For example, take a random 4 digit random number like 5129. Rearrange the
numbers from highest to lowest. 9521 - 1259 = 8262. Now repeat the process with your answer of 8262. You always come back to 6174 within 7 iterations or less.

[tomtke]

Fractions like algebra equations rely on the concept of apples to apples and oranges to oranges.

In this problem we have two different denominators of 4 and 8. To sum these two fractions requires EQUAL denominators.

(1/4)-(5/8)
=
(2/8)-(5/8)
=
-(3/8)

ALTERNATELY... BOW-TIE

(1/4)-(5/8)
=
((1×8)-(4×5))/(4×8)
=(8-20)/32
=-12/32
=-6/16
=-3/8❤✔️

This 2nd method ALSO results in SAME denominator = 32.
as in...
Forcing the two fractions to have same denominator is achieved by multiplying the two denominators together.
I.e. 4×8=32
then multiply BOTH fractions by (32/32)
I.e.
(32/32)×{(1/4)-(5/8)}
=
(32/32)(1/4)-(32/32)(5/8)
=
(8/32)-(20/32)
=-12/32
=-3/8✔️

[FioLolo-fijy]

people in the comments not realising that no one cares if you can do it. its for people who need it. get over yourselves.

[RenitaSeals]

You need a common denominator for both fractions.

[Ichijoe]

So this is NOT about finding the soapy LCD, but the balance of the denominator. Not that (as was painted out earyish in the video), is any simpler. But at least had my maths Teacher managed to convey that thought across. I might not have this irrational hatred for all things Fractions.

Mores the reason to be thankful to be an Expat who lives in an Albeitlly Metric, but largely Fraction free lifestyle.

[claudelett]

Please show us how to find square roots without a calculator.

[Gate_Seven]

1/4-5/8=
(2/2)*(1/4)-5/8=
(2-5)/8=
-3/8

[vincentrobinette]

2/8-5/8=-3/8. the "bowtie" method is the best way to do it, if you're dealing with numbers with huge low common denominators. Just imagine trying to 7/17 from 15/41. Bow tie rules!

[maryogie]

It takes 10 seconds to solve this problem.

[gavindeane]

How can you talk for so long about the bowtie method without explaining WHY it works???

It's not like it's difficult to explain, but you're just giving people some mysterious magic trick that they're just supposed to learn by rote and remember.

[Nightcrawler]

This teacher is very very lousy one. He’s trying to sell his products.