3/15 – 3/10 =? Understand Fractions? Let’s test your basic math skills!

Help with Middle and High School Math
Test Prep for High School Math, College Math, Teacher Certification Math and More!

Popular Math Courses:

Math Foundations

Math Skills Rebuilder Course:

Pre-Algebra

Algebra

Geometry

Algebra 2

Pre-Calculus

• MIDDLE & HIGH SCHOOL MATH
• HOMESCHOOL MATH
• COLLEGE MATH
• TEST PREP MATH
• TEACHER CERTIFICATION TEST MATH

[richardhole]

In this case the hard way is as fast as seeking a shotcut. LCD is 30
6/30 - 9/30 = -3/30 = -1/10

[kittyskid]

paused at 1:47. Got it right. Reduced 3/15 to 1/5; making the CD 10. Therefore 2/10-3/10. Result -1/10. Now on to the video to see how I did.

[mylittlepitbull]

I did it in my head in 3 seconds way different than anybody else would.
3/15 is 1/5 - 3/10 (which is 1.5/5) = -.5/5 = -1/10

[vincentrobinette]

I didn't think to reduce 3/15 to 1/5, I just simply set the LCD at 30, and multiplied the 3 with 2 to get 6/30, multiplied the 3 with 3 to get 9/30. That gave me -3/30, which reduced to -1/10. That's a clever idea, to reduce the fractions first, to get the lowest possible common denominator, making it easier to solve in your head: No calculator, no "scratch" paper!

[thomasharding]

Fractions are fUN! You pointed out the problem if it had been 7/15 which is why I always go the direct route of LCD and do the reductions at the end. Nice Explanations.

[Save]

Having been a kid in the 1970's, there is a lot I have forgotten. Thank you for such quality math videos. 🏆

[robertloveless]

TO FIND LCD AND GCF, use a venn diagram. Factor both numbers to their primes, put the ones they share in the 'common' area, the ones they don't share on the outsides. SHARED factors multiply to make GCF, ALL FACTORS multiply to make the LCD.
I can't make an venn here, so bear with me. 24 and 36, eg. ----
24 = 2×2×2×3
36= 2×2×3×3.
They share two 2s and one 3.
Diagram would be [2 (2, 2, 3) 3]
Ergo, GCF would be 2×2×3 and LCD would be 2x2x2x3x3.
BTW, the LCD × GCF. ALWAYS = the product of the 2 original numbers. And the reduced fraction is ALWAYS the outside numbers (in this case, 2 and 3)

[jamescoe]

I would have never became a civil engineer if you were my first math teacher.

[toma.pudding]

I thought this was some sort of tricky question because of the thumbnail claiming that many will get it wrong! Turns out it was really basic. Regardless I am happy with reviewing basic math skills. It is important to keep the foundations strong

[tom-kzpb]

You can also cross-multiply: (30/150) - (45/150 ) = (-15/150) = -1/10

[bigdog]

super easy I will use negative exponents to represent fractions
-3(10 ^ -1) + 3(15 ^ -1) [ here I am saying negative three tenths plus three fifteenths]
-9(30 ^ -1) + 6(30 ^ -1) [Here I recognized the lcd is 30 and changed the fractions so they had common denominators]
30 ^ -1 * (-9 + 6)
-3 (30 ^ -1)
-1 (10 ^ -1)

Final answer is negative one tenth

[MrMousley]

Well (just looking at it) 3/10 is bigger than 3/15 so the answer is going to be 'minus'
then (quickly in my head) 3/15 - 3 /10 is 6/30 - 9/30 = - 3/30 which is - 1/10
or 3/15 is 1/5 which is 2/10 giving us 2/10 - 3/10 which is - 1/10

[robertloveless]

Anybody out there old enough to remember the "means and extremes"?.
A/B + C/D = (AD) + (BC) / BD. Works with subtracting, too.
3/4 -1/6 = (3×6) - (1×4) / (4×6). reduce.
Easy- peasy.

[OVHabitats]

While you were learning math in 1977 I was in college and soon after in the military however, I always enjoyed math and that is why I love your channel. Every time one of your videos pops up I have a need to test myself. For the record, I usually have the right answer. I knew Aunt Sally too.

I always equate math with money or food. LOL Fractions are pizzas and +/- numbers are a check book. My mother had an issue with negative numbers until I asked her to bring her check book over and I asked her you have $750 in your checking account and you write a check for $800 what do you do? Her response was priceless. She said I have to run like hell to the bank and deposit at least $50. Yep, that is your negative number.

[Hewhowalks-fvmq]

Love doing mental maths keeps the brain going

[davesaftrains]

Having been a scientific programmer and statistician I rewrite the expression as (3x(1/15)) - (3x(1/10)) then apply order of precedence or operations (and a calculator 😮 (😢)) arrive at -(1/10) 😃 🧮

[stevestephens]

The easiest and quickest way the solve this is to multiply the left term by one in the form of 2/3 over 2/3, resulting in 2/10 - 3/10 = 1/10.BTW I got my math degree exactly fifty years ago.

[russelllomando]

got it -1/10 easy LCD of 30 subtract to a -3/30 reduce thanks for the fun

[tomtke]

Alternate--
(3/15) - (3/10)
(1/5) - (3/10)
(2/10) - (3/10)
-(1/10)

[terry_willis]

I solved this one in my head while swimming under water across my pool.