Maths help please!

[DeceitfulMummy]

Looking through DS's homework. The top one is correct - according to him he did it in class with the teacher. I don't see why it's correct but also can't figure out what it should be. And the others? What obvious thing am I missing? It's a long time since I did maths!

2n+1 is the pattern

The top number being 'n' and the answer under it

X2 plus 1

😳 ok now I feel stupid! How do you figure that out though? Is there a way of setting up an equation or are you just supposed to recognise it? And the other two?

Second must be 120/n

@Cooroo how did you figure that out?

How do I explain to DS how to figure out what the pattern is?

Final one is n/3

Plenty of videos on nth term on YouTube which should explain how to do the first one at the least

It can’t be that

The final one is 3n/10, not n/3

OP, I think these are pretty nasty, and I have a PhD in physics. May I ask how old your son is?

What does n/3 or X2 + 1 even mean

Just explain how on earth to work out the 2nd and 3rd line to us

What does 3n/10 even mean

Op how old is your son (panicking here!!)

If n is the number in the top line, then 3n/10 is how you get the number in the bottom line. So if n is 5, then 3x5/10 = 1.5. If n is 50, then 3*50/10 = 15.

This is why I asked the son's age - I don't think these are easy to work out.

Brilliant thank you

I’m still trying to work the second one out! Is it gcse or A level?

Yr7 (prob with dyscalculia so won't "see" any kind of pattern in numbers).

In primary his teacher didn't really make him do any maths so this is a shock to the system. I don't know how to explain it to him either. He has a test on Friday, how do I give him a "method" to deal with this type of question? @whoateallthecookies How did you figure that out, or did you just see it?

My y7 has just started learning n terms in maths, it must be on the curriculum as my DD remembers doing it as well. I really struggled to get my head round it and don't remember doing it in school myself all those years ago!

@Candymay Why can't it be 120/n? That seems to apply to the filled-in examples.

In primary his teacher didn't really make him do any maths

That's terrible! Why on earth not??

The homework above is inappropriate for a Y7 (let alone one weak at maths) and I'm not surprised he's struggling. Send a note in saying he couldn't do it nor did it say in his book how to tackle it so you were also unable to help.

Write down the differences between the numbers in the top row....and the differences between the numbers in the bottom row, for example - take the third question
5-1=4
15-5=10
40-15=25
50-40=10
x-50 = y
120-x = z
500-120=320

1.5-p = q
4.5-1.5=3
12-4.5=7.5
15-12=3
24-15=9
r-24=s
t-s=u

Put the two sets of differences next to each other to see the relationship between them

4 -> q
10 -> 3
25 -> 7.5
10 -> 3
y -> 9
z -> s
320 -> u

imagine two ladders next to each other - the rungs are spaced differently - you have to stretch or compress one ladder to make it the same spacing as the other ladder - imagine one ladder has rungs spaced 10cm apart and the other has rungs spaced 3cm apart (10 -> 3 appears twice in our list of differences) - you have to change the scale to make one ladder have the same spacing as the other - you have to rescale - you have to multiple one spacing to get the other spacing so what do you multiple 10 by to get the answer 3?

10 x 3/10 = 3

So this number 3/10 is the scaling factor and is the number that goes in front of n

now check to see what happens when you multiple n=50 by 3/10 = you do get 15
50 x 3/10 = 15

so the two rows of numbers are in a simple proportion to each other. Tick the box.

Please don't attempt to get your Y7 to understand larkstar's very well meaning but age-inappropriate explanation!

So sorry! My basic maths couldn’t work it out even when given the answer! Of course it is 120/n
sorry!!!!
yr 7 though?! Wow. My children are a bit older. Pretty sure they wouldn’t be able to do this. I’ll have to ask them and see

I love this. Thank you

I think the ‘proportional’ box may be the key to this. Has he been learning about that? The numbers are proportional if doubling the number in the top row also doubles the number in the bottom row. It doesn’t have to be doubling, as long as its the same multiplier for top and bottom. So eg in the 3rd series, 5 x3 = 15 and 1.5 x3 = 4.5. That should help to fill in the gaps.

1st row 2n + 1
Trying to work this one...
I got the 3rd row 3n/10 .