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Can anyone help me with DSs math's problems

(11 Posts)
iamnotaponceyloudperson Wed 17-Jun-15 13:03:18

I'm working through Bond books with DS and try to make sure i understand the problems first. I am a complete dunce at maths so these probably seem so easy to most of you!

Can anyone break down the maths for these as I keep getting the answers wrong...

1. If 8 people can do a certain job in 10 hours, how long would it take 20 people to do the same job working at the same speed?

2. 36 lamposts were spaced evenly along a road that was 1.575km long. What was the distance in metres between each pair of posts?

For 2 divided 1.575 by 36 and get 43.75 but the answer is 45 and I don;t get it!!!!!!

Thank you so much.

tumbletumble Wed 17-Jun-15 13:07:19

1. Total length of time = 80 person hours (8x10=80). So 20 people will take 4 hours (80/20=4)

2. It's a bit of a trick as you need 1 lamppost at each end, so there are only 35 gaps between lampposts (which is what takes up the space). 1575/35 = 45

Trizelda Wed 17-Jun-15 13:09:35

I can help with the second question. They always put these in...sometimes lamp posts sometimes fence posts! If you imagine a ruler with the lamp posts spread evenly, the first one will be placed on the number '0' and the remaining 35 will be spread over the distance. Therefore 1575 divided by 35 equals 45 (i think!).

FeelingSmurfy Wed 17-Jun-15 13:10:35

1) 8 people take 10 hours, so 8 X 10 = 80 hours total
80 hours ÷ 20 people = 4 Hours

FeelingSmurfy Wed 17-Jun-15 13:11:59

2) you start with one lampost without a gap before it, so there will only be 35 gaps

iamnotaponceyloudperson Wed 17-Jun-15 13:13:40

Oh my goodness, how stupid am I. Thank you!!!!!!!

Would you mind doing one more as I really can't get this. This will be the last one I promise but I need to work out a formula so I can apply it to other similar ones..

A cashbox contains some coins to the value £5.25

There are twice as many 5p coins as 2p coins and twice as many 2p coins as 1p coins. How many 5ps, 2ps, and 1ps are there?

Thanks again, last one I promise. I missed loads of school as a child due to ill health,caught up in everything but maths totally and utterly defeats me as I missed so any corner stones.

tumbletumble Wed 17-Jun-15 13:19:03

let C = no. of 1p coins

There are C 1p coins, 2xC 2p coins and 4xC 5p coins

C x 1p + 2 x C x 2p + 4 x C x 5p = 525p
25 x C = 525
C = 21

ie 21p in 1p coins (21 of them), 84p in 2p coins (42 of them) and 420p in 5p coins (84 of them)

lucyanntrevelyan Wed 17-Jun-15 13:20:31

Start with one 1p, 2 2ps and 4 5ps. Add them up to give you 25p. (4x5=20, 2x2=4, 1x1=1)
Then work out how many 25p in £5.25 = 21
So you have 21 1p, 42 2p and 84 5p.

addictedtosugar Wed 17-Jun-15 13:21:53

Last question: your trying to find the value of X, and in your box you have

X(1p coins) + 2X(2p coins) + 4X (5 p coins). And that comes to �5.25.

So, X*1 + 2X*2 + 4X*5=525
25X=525 so X= 21.

21 1 p coins, 42 2 p coins and 84 5p coins

Radiatorvalves Wed 17-Jun-15 13:27:58

I'm no maths expert, but looking at those figures, check the pattern
2x2p = 4
4x5p = 20

Ie in total, that = 25p

You get 21 x 25p in £5.25

So answer is

21. x 1p = 21
42 x 2p = 84
84 x 5p = 420

I think!

iamnotaponceyloudperson Wed 17-Jun-15 13:37:52

Thank you to all you wise people.

I have a very good arts degree but in my day if you could scrape to CSE1, you could escape maths forever....or so I thought!

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