Math Is Fun Forum

roel

Member

Registered: 2006-07-22

Posts: 48

problem solving

hi.. can you please help me with these problems?

1. If it takes 12 days for 6 men to finish a job, how many more men will it take to finish the same job in 8 days assuming that they work at the same rate?

2. A ton of ore contains 18% iron. How many tons of ore, to the nearest 10 tons, will yield 25 tons of iron?

3. At the end of the school year, the average grade of X in all his 7 subjects is 82. If her grade in physical education is not included in the averaging, her average grade will be 83. What is her grade in Physical Education?

4. Sarah is 20 years older than her brother at present. When Sarah got married 5 years ako, she was twice as old as her brother. How old was Sarah when she got married?
               
Please help... I really need to learn this.. Help me enter a good law school...

Identity

Member

Registered: 2007-04-18

Posts: 934

Re: problem solving

1.

Let x represent a complete job:

6 men can finish 1/12 of a job in 1 day.

1 man can finish 1/72 of a job in 1 day.

Now, if we want n people to complete x in 8 days:

Therefore it will take 9 men to finish the job in 8 days, 3 more than before.
(I went a bit overboard in showing the working, you don't need to do it like this)

2.

Let m(x) denote the mass of x.

Now using equal ratios, we get 25 tonnes of iron with x tonnes of Ore.

To the nearest ten tonnes, this is 140 tonnes of ore.

edit: added 3 and 4:

3.

Let the grade of X for sport be a. Let the grade of X for all his other subjects be b. Then,

...1

...2

...from 2

...from 1

Therefore her grade for sport was 76.

4.

Let S be sarah's age and B be her brother's age.

...1

...2

...2'

...substituting 1 into 2

So Sarah was 45 - 5 = 40 years old when she got married.

Last edited by Identity (2007-11-23 22:08:13)

roel

Member

Registered: 2006-07-22

Posts: 48

Re: problem solving

hey... thanks for the help... BUT, I still have more problems here.. Is it okay if i will post it here again?

Identity

Member

Registered: 2007-04-18

Posts: 934

Re: problem solving

I think you might have to start a new topic, you know, just to keep things neat in the forum.

roel

Member

Registered: 2006-07-22

Posts: 48

Re: problem solving

I think you might have to start a new topic, you know, just to keep things neat in the forum.

hey.. thanks....