Trying to “help” with some maths revision, its been along time since I’ve done anything like this.

Can anyone help with the following:

3(2x + 4) = 5x + 17

I’ve got this far:

3(2x + 4) = 5x + 17
6x + 12 = 5x +17
6x = 5x + 5

So *if* I’m correct thus far Im confident that x = 5. But i wouldn’t be certain how to show my working.
And I’m not that confident Im actually correct 🙄

Thanks

That’ll do and you can be sure you’re correct as 5 satisfies the original equation.

You’re a natural 🙂

Spot on

‘shudders’

🙁

what would be the step to get from

6x = 5x + 5
to
x = 5

for the purposes of explanation…
I know its x = 5 in my head, but cant show how i arrived at that

The only ‘improvement’ (and it would be very marginal) is that your last bit is inferred as opposed to shown:

6x = 5x + 5

Subtract 5x from both sides

=> 6x-5x = 5

X = 5

Unless I’m hopelessly out of date, I would expect that they would want to see the intermediate workings, which if things have remained unchanged since I was at school (unlikely), would mean something like this:

6x + 12 = 5x + 17
6x – 5x = 17 – 12
x = 5

Thanks all!
Might be back later with some more! :-/

Remember to try and get all the variables on the left of the = and the numbers on the right. I’m sure there’s probably a name for that process…

sod off – we’ve shown you how to do it, you’re on your own now.

(can someone help my daughter with % calcs. I can do them but I can’t explain adequately to get her to see it. Seriously; it’s not the calcs themselves, it’s knowing when to use which:

eg: Polly sees a dress in the shop. The label price is £15 but there is a special offer of 20% off. How much does the dress cost?

Ans: £15 x 20% = £3, therefore dress is 15-3 = £12
(or – 20% off means you pay 100-20 = 80%. £15 x 80% = £12)

vs

Polly buys a dress in the 20% off sale. She pays £12 for the dress, what was the original price.

Ans: £12 / 0.8 = £15

But she keeps using £12 x 1.2 to find the original price = £14.40 = wrong.

vs: Polly buys a dress in America and can claim the sale tax of 6.5% back. The price she pays is $15.97, what was the cost of the dress without tax

Ans: $15.97 / 1.065 = $15

But she keeps using £12 x 1.2 to find the original price = £14.40 = wrong.

get her to do a really obvious one like 50% discount on a tenner – with real pound coins

gauss1777

Interesting user name on a maths thread 🙂

she can do the first no probs, it’s flipping it to back calculate it.

And in fact if I get her to do the first one first she then sees the second. But give her the second in isolation, she has a mental block.

“Polly buys a dress in the 20% off sale. She pays £12 for the dress, what was the original price.

Ans: £12 / 0.8 = £15″

I like your method best,

perhaps a slight tweak to 0.8x=12
x=12/0.8
X=15. where x is the original amount would make it clearer why you divided?

but I have often seen it taught:

80%——— 12
1%————12/80=0.15
100%———-100×0.15=15

Hope that’s clear.

Oh and Rob, I’m a Gauss fanboi – as they say

Ta, will try it.