Maths homework question query

(12 Posts)
littlenicky61 Thu 25-Feb-16 11:16:04

Just looking for someone who is better at maths than me to double check one of my daughters maths answers as she not 100% sure she got it right .

Question :
A can has a height of 11cm and radius of 3.5cm. The label covers the entire height of the can and the label has a 1cm overlap vertically so that it can be stuck together. Calculate area of label.

I think its the mention of the vertical overhang that has made her question herself so thought I'd check with the Mumsnet mums !

Answer :

Area of label = h x pi x d = 11 x pi x ( 7cm + 1cm ) = 276.46 cm2

Many thanks !

DadDadDad Thu 25-Feb-16 14:37:03

Not quite. The diameter has not increased by 1cm, the circumference has, so you want:
11 x (pi x 7 + 1) = 252.9 sq cm

DadDadDad Thu 25-Feb-16 14:39:52

And a maths question in Unanswered Messages - you made my day (ex-maths teacher, nice to dabble occasionally smile).

PurpleDaisies Thu 25-Feb-16 14:44:33

The way I'm picturing it the vertical overhang bit means the height has increased by 1cm. Using the formula for surface area of a cylinder
I'd do (11+1)X pi X (3.5x2).

RafaIsTheKingOfClay Thu 25-Feb-16 14:46:06

I agree with DadDad.

If there's no diagram, it might help her to sketch one quickly so she can see where the over hang is.

PurpleDaisies Thu 25-Feb-16 14:46:25

But it could easily be what daddaddad says-I'm not sure the question is particularly clear. I'm another germ who likes maths puzzles (I teach maths too).

PurpleDaisies Thu 25-Feb-16 14:48:50

Wait-it says overlap not overhang-I'm changing my answer to 11+(2x3.3xpi+1)

RafaIsTheKingOfClay Thu 25-Feb-16 14:49:31

I think it's the way the question is worded, purple. It isn't particularly clear what it is talking about. It does sound like it should be overhanging the bottom of the tin but that wouldn't make any sense in terms of sticking the label together.

DadDadDad Thu 25-Feb-16 15:36:38

I suppose if it said "vertical overlap" that would be slightly less ambiguous, but it's clear to me, it's like the label on a jam jar, with a height of 11 cm then wrapping all the way round plus another cm so that an overlap exists running vertically down the tin.

littlenicky61 Thu 25-Feb-16 23:12:46

Thanks for all your responses sorry only just had chance to read them . Sorry toi it should have been vertical overlap not overhang !! And it said can of baked beans if that changes anything ? Will that change things again or is daddaddad correct with 252.9. Thanks again to you all: )

senua Thu 25-Feb-16 23:23:12

If you use pi=22/7 then it comes out to a neat 253.

lougle Fri 26-Feb-16 00:05:06

I agree with DadDadDad, but I'd want her to understand why it's 11 x (pi x 7 + 1) so I'd break it down:

The area of the tin surface is h x pi x d

So 11xpix7=241.9

The overlap has nothing to do with the tin itself. It's just a 1 cm rectangle of extra paper attached to the end. So that is h x w

11 x 1= 11

Total area: 241.9 + 11 = 252.9 cm^2

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