Groucho's Fact Hunt

[Jamo Martinez]

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That. is. brilliant.

 

[Groucho]

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Does this work in every instance?

 

[scratchnsurf]

Does this work in every instance?

Yes. It's essentially a multiplication and they can be done in any order with the same resulting product.

To find 25% of 8, the multiplication is 25 X 0.1 X 8.

To find 8% of 25, the multiplication is 8 X 0.1 X 25.

The result is the same.

 

[Tramps_mate]

That. is. brilliant.

Does this work in every instance?

I'm quite fond of numbers and number patterns (yes its sad). I was staggered to learn this!!

I can't believe I'd not heard or realised this before..

 

[Jamo Martinez]

I'm quite fond of numbers and number patterns (yes its sad). I was staggered to learn this!!

I can't believe I'd not heard or realised this before..

Can't believe none of the teachers in school ever told us. my wife and son were just as surprised.

Or maybe it's only recently been discovered.

 

[scratchnsurf]

Yes. It's essentially a multiplication and they can be done in any order with the same resulting product.

To find 25% of 8, the multiplication is 25 X 0.1 X 8.

To find 8% of 25, the multiplication is 8 X 0.1 X 25.

The result is the same.

Should have put 0.01, not 0.1.

 

[PITA]

Blown my mind that one!!! I cant believe ive never known this!!

If you think of it as 0.08 x 25 and 0.25 x 8 then it is more obvious.

 

[Jamo Martinez]

Yes. It's essentially a multiplication and they can be done in any order with the same resulting product.

To find 25% of 8, the multiplication is 25 X 0.1 X 8.

To find 8% of 25, the multiplication is 8 X 0.1 X 25.

The result is the same.

Shouldn't that be 0.01?

 

[kev]

Shouldn't that be 0.01?

He already spotted it

Should have put 0.01, not 0.1.

 

[deipnosophist]

I learnt that rule in form 2 (year 8). Ken Morris was our teacher and he was very good.

 

[chrismpw]

I never knew this until this thread. Then again I was told at school that "of" meant times (multiply). So 4 x 3 is the same as 3 x 4 ... it makes sense that way. So 40% x 3 is the same as 30% x 4.

 

[Jamo Martinez]

He already spotted it

Soz about me. I'd still only had one coffee at the time.

 

[BNJ1878]

I excitedly told this percentages thing to my incredibly bright Chinese partner.

I thought it was the equivalent of discovering fire, she thought I had a bang on the head.

"it's basic multiplication. It doesn't matter what order the numbers are, the result is the same"

I mean, she's right..... But I didn't even get a pat on the head.

 

[Jamo Martinez]

I excitedly told this percentages thing to my incredibly bright Chinese partner.

I thought it was the equivalent of discovering fire, she thought I had a bang on the head.

"it's basic multiplication. It doesn't matter what order the numbers are, the result is the same"

I mean, she's right..... But I didn't even get a pat on the head.

That's the thing. In school, we learned to divide by 100 after multiplying the other 2 numbers.

Once it's pointed out, it's obvious that multiplying by 0.01 is the same as dividing by 100. I'd just never considered it as solely multiplication.

Clever people see the simple things.

 

[PhilM]

That's the thing. In school, we learned to divide by 100 after multiplying the other 2 numbers.

Once it's pointed out, it's obvious that multiplying by 0.01 is the same as dividing by 100. I'd just never considered it as solely multiplication.

Clever people see the simple things.

I don't think it's as clear cut as that, and the relationship for percentages hasn't recently been discovered.

I have a relative who works for a DfE funded maths organisation (the NCETM), and they regularly say the teaching of Maths in this country has been (and is) dire.

The common arguments are that it's been superficial (surface level), too much breadth and not enough depth and learning by rote rather than understanding.

The Chinese system, which we're apparently trying to adopt, is based on depth rather than breadth, building conceptual understanding and building links.

In layman's terms, they are better at maths because they've been taught how and why things work, including links to other content, before actually applying it.

We were taught how to complete arithmetic processes rather than truly know what is happening, which means we struggle to translate content into context.