Tutor MathsGuru: Ask me for your burning Maths questions!

[MathIzzzFun]

kwcllf:

Hi please help



When k patners b, they take 8 days to paint a house. When b patners h, they take 6 days to paint the house. When h patners m, they take 12 days to paint a house. How many days do k and m take to paint the house together?

Thanks

Total work required to paint a house --> 120 units
K+B --> 120 units/8 days = 15 units/day
B+H --> 120 units/ 6 days --> 20 units/day
H+M --> 120 units/12 days --> 10 units/day
K+B+B+H+H+M --> 45 units/day
K+M --> 5 units/day (B+H --> 20 units/day)
120 units --> 120/5 = 24 days

K+M will take 24 days to paint the house.

cheers.

[kwcllf]

MathIzzzFun:

kwcllf:

Hi please help



When k patners b, they take 8 days to paint a house. When b patners h, they take 6 days to paint the house. When h patners m, they take 12 days to paint a house. How many days do k and m take to paint the house together?

Thanks

Total work required to paint a house --> 120 units
K+B --> 120 units/8 days = 15 units/day
B+H --> 120 units/ 6 days --> 20 units/day
H+M --> 120 units/12 days --> 10 units/day
K+B+B+H+H+M --> 45 units/day
K+M --> 5 units/day (B+H --> 20 units/day)
120 units --> 120/5 = 24 days

K+M will take 24 days to paint the house.

cheers.

Hi,

Wonder if you could enlighten me if I solve the question in the following manner:

K+B= 8 ------ (1)
B+H = 6 -------(2)
H+M = 12 -----(3)

(1) minus (2) ----> K-H = 2 -----> H = K-2, substitute into Equation (3)

H+M =12
(K-2)+M = 12
K+M = 14

The answer is different from your solution. Is there something wrong with my solution? Thanks!

[MathIzzzFun]

kwcllf:

MathIzzzFun:

[quote=\"kwcllf\"]Hi please help



When k patners b, they take 8 days to paint a house. When b patners h, they take 6 days to paint the house. When h patners m, they take 12 days to paint a house. How many days do k and m take to paint the house together?

Thanks

Total work required to paint a house --> 120 units
K+B --> 120 units/8 days = 15 units/day
B+H --> 120 units/ 6 days --> 20 units/day
H+M --> 120 units/12 days --> 10 units/day
K+B+B+H+H+M --> 45 units/day
K+M --> 5 units/day (B+H --> 20 units/day)
120 units --> 120/5 = 24 days

K+M will take 24 days to paint the house.

cheers.

Hi,

Wonder if you could enlighten me if I solve the question in the following manner:

K+B= 8 ------ (1)
B+H = 6 -------(2)
H+M = 12 -----(3)

(1) minus (2) ----> K-H = 2 -----> H = K-2, substitute into Equation (3)

H+M =12
(K-2)+M = 12
K+M = 14

The answer is different from your solution. Is there something wrong with my solution? Thanks![/quote]hi
this is a work rate question... so, have to work on per unit time basis.
eg we use K+B+H+M --> 20 -- this means that all four working together will take 20 days to complete the job, which is incorrect.

If all are working together, we expect that time taken will be less...therefore, need to work on per unit time basis eg if A complete the work in X days, and B completes the work in Y days, then X will complete 1/X of the work in 1 day, and B complete 1/Y of the work in 1 day and both A & B will complete (1/X + 1/Y) of the work in one day.

cheers.

[Herbie]

I hv one qn.


On a map, an area of 200 cm sq represents an actual area of 8km sq
A. Ifthe map has a scale of 1:k, find the value of k
B. If the distance between two points on the
map is 3cm, find the actual distance in km between two points.

Can show the steps pls? Tq

[MathIzzzFun]

http://i46.tinypic.com/s15mkw.png\">


cheers.

[Herbie]

MathIzzzFun:

deleted

Hi noted u hv deleted yr answer.

[MathIzzzFun]

MathIzzzFun:

http://i46.tinypic.com/s15mkw.png\">


reposted

cheers.

[Herbie]

MathIzzzFun:

MathIzzzFun:

http://i46.tinypic.com/s15mkw.png\">


reposted

cheers.

Thanks! I have another maths qn but i am not able to upload the pic. =(

[VivianChan]

Hi I need help,


Linda could bake 5 cakes each day. Sally could bake 8 cakes each day. If Sally was sick for 3 days, how many days would she need to bake 12 more cakes than Linda?

Thanks!

[MathIzzzFun]

VivianChan:

Hi I need help,


Linda could bake 5 cakes each day. Sally could bake 8 cakes each day. If Sally was sick for 3 days, how many days would she need to bake 12 more cakes than Linda?

Thanks!

Assuming that both start on the same day and then Sally was sick for 3 days. If they started on different day, the solution will be different.

5 x 3 = 15 ---> Linda would bake 15 more cakes than Sally for the 3 days that Sally was sick.

8 - 5 = 3 --> Sally bake 3 more cakes than Linda every day.
To bake 12 cakes more than Linda, Sally will need to bake (12+15)= 27 more cakes --> 27/3 = 9 days

Sally need to bake for 9 days to have 12 more cakes than Linda
ie Sally bakes for 9 days, Linda bakes for 12 days.

cheers.