A maths question (from a 10 year old's homework)

[parakitaMol.]

OK.

It's been a while since I did maths homework.... but this one that my husband's 10 year old daughter has been given, has me rather foxed...

practise paper said:

Ben and Emma each start to grow a plant on the same day.

After 1 week the plants are 5cm tall.

During the next three weeks Ben's plant grows f centimetres per week and Emma's grows g centimetres per week. Emma's plant is taller.

When the plants are 4 weeks old. How much taller is Emma's plant than Ben's, in centimetres

I think the answer is an equation something like 20cm + (g-f)
But they have not done equations yet. And it seems too advanced.

What's the answer???

....and how do you work it out - it's really annoying me. Can someone explain so that I can relay it to a child - there are 5 adults in the house right now and none of them know this one!

[ewenm]

3*(g-f) isn't it?

So each week the difference is g-f and it's going for 3 weeks...

[Fetchez la vache]

(5cm + 3g) - (5cm + 3f) cm
?

[Fetchez la vache]

ewenm said:

3*(g-f) isn't it?

So each week the difference is g-f and it's going for 3 weeks...

yep. i vote this

[parakitaMol.]

You can't answer this with a question!!!

[Parsnip]

I may be being dim, but i would read it like this:

difference = 3*(g-f)

The starting 5cm doesnt make count for anything, and the difference between the two is g-f per week, you have 3 weeks.

[Justayellowbadge]

3(g-f)

There isn't enough information for a numerical answer.

[Parsnip]

bloody hell, some people can type hella quick...

[TheStig44]

Fetchez la vache said:

(5cm + 3g) - (5cm + 3f) cm
?

Thats what I thought it was. Although seems a somewhat advanced answer for a 10 year old...

[ewenm]

OK if you want detail, after 1 week both are 5cm. Then his grows at f per week for 3 more weeks so is 5+3f cm. Hers grows at g per week for 3 weeks so 5+3g cm after 4 weeks.

Difference: 5+3g - (5+3f) = 5+3g-5-3f = 3g-3f = 3(g-f).

Edited by ewenm on Thursday 16th July 18:23

[Poledriver]

3(g-f)

HTH (If it's right!)

[Shaw Tarse]

Ben is male he forgot to water the plants, they're all dead

[Fetchez la vache]

Shaw Tarse said:

Ben is male he forgot to water the plants, they're all dead

[grumbledoak]

I'm feeling like an echo, but...
It is 3g - 3f, or 3x (g-f)

To explain it, each plant gets three times a weeks growth. But, we only know the growth rate as g and f, so you cannot get 'proper' numbers out of this question. As a youngster this might be a little frustrating (they normally start you off with round number questions), but maybe that is the point?

[Famous Graham]

TheStig44 said:

Fetchez la vache said:

(5cm + 3g) - (5cm + 3f) cm
?

Thats what I thought it was. Although seems a somewhat advanced answer for a 10 year old...

The 5cm is irrelevant as it's the same for both.

[Syd knee]

42

[ribenavrs]

Syd knee said:

42

[Poledriver]

MX5

[parakitaMol.]

Brilliant. Thanks for the contributions....

I didn't think the first week or the 5cm were part of the answer - and yes I agree this particular question is a bit too advanced for a 10 year old.

[bonsai]

Anyone else pleasantly surprised to see that for once, a maths question does not feature 2 ethnic names like they so often do, in order to appear PC.