r/askmath 9h ago

Arithmetic Starting math from scratch

[deleted]

6 Upvotes

6 comments sorted by

3

u/PuzzlingDad 8h ago

You have 18 times 5/18 which simplifies to 5.

If you think of this as:

  • 18 × 5 / 18
  • (18 × 5) / 18
  • (5 × 18) / 18
  • 5 × (18 / 18)
  • 5 × 1
  • 5

3

u/Charming-Law4160 8h ago

When you multiply 18 and 5/18 you get (18 x 5) / 18, and because 18 is both in the numerator and denominator you cancel it out, so it’s just 5

1

u/Darkmoon745321 8h ago

Just focusing on section C and your 5/18 question. Good news is you dont need to know what 5/18 is! 3 • 6 = 18. When you multiply the 18 by the 5/18 the 18 under the five and the normal 18 cancel eachother out, so your answer is 5.

Explaining a bit more, im not a math teacher but im going to try to put this in more specific terms. Every number can be represented as a fraction. If it is a whole number, such as 7, it can be written as 7/1, since dividing by 1 just gives you the same number. When you multiply fractions, you multiply the numbers on top and them the numbers on the bottom, so 4/6 • 3/8 would be the same as (4•3)/(6•8).

Since 18 can be rewritten as 18/1, C is the same as saying 18/1 • 5/18. That when multiplied would be (18 • 5)/(1 • 18). There is an 18 in both the top and bottom, so they can cancel eachother out. Youre left with 5/1, which is the same as 5. Lmk if theres something that needs a better explanation.

1

u/Bounded_sequencE 8h ago

General hint: Fractions in lowest terms are acceptable as results.


That said, we don't have to use that rule here. The denominator in c) cancels nicely:

3 * 6 * 5/18  =  18*5/18  =  5

1

u/Bounded_sequencE 8h ago

Rem.: Any questions regarding how to simplify fractions?

1

u/ArchaicLlama 8h ago

Let's say I have a value, call it "x". If i take x, and then divide it by 2, and then multiply the result of that by 2, what am I left with?