Maths Question

[angchuk]

Hello

I am finding it very difficult to answer this question:

Mary is 12years old and her father is 42. Answer these questions:
(a) How old was Mary’s father when he was 4 times as old as Mary?
(b) In how many years’ time will her father be 3 times as old as Mary?
(c) How old will Mary be when her father is 10 times as old as Mary was 6 years ago?


Please help

Thanks

[First-timer]

a) 40 b) 3 c) 30

[yoyo123]

Mary age =x
Dad's age = x+30.

to find out how old he was when he was 4 x mary's ge

x+30 =4x
30 = 4x -x = 3x

30 =3x

therefore x= 10.

if Mary was 10 he was 40

B:

if mary is 12 now and he is 42
next year 13 and 43
2 years 14 and 44
3 years 15 and 45 45=3 x 15 so in 3 years time he will be 3 x older than her


C;6 years go Mary was 6 , so her father will be 60 .

we know he is 30 years older than her, so she will be 30

[angchuk]

Thank you, First timer and Yoyo for the explanation.

[sherry_d]

These are the questions I really find difficult. I can happily work out an equation if its given as an equation but when its written like this I get completely thrown out. Not suprisingly my DD is struggling with these too. Is there any resource that you can recommend or worksheet that me and DD can get more practice on where they have these sort of equation. A while ago someone recommended WHS KS3 worksheet but I failed to locate them. I particularly want them wordy like these not as straight equations.

[JaneEyre]

Sherry,

I don’t know if it helps but I directly changed these sentences into equations, including also a ‘y’ for the dad’s age... So I have the same way of reasoning as yoyo except for the second question where I ‘think’ in term of equations instead of a trial/error method...
So here is how I thought (sorry for the repetitions, yoyo, our way do coincide but it is this habit of converting phrase into equations which might be useful to sherry)...

Mary is 12 years old and her father is 42.
→ Mary 12 now, but I choose ‘x’ to represent her age
Father 42 now, but I choose ‘y’ to represent his age
From the above information, I know that : y-x=30

Question a ) How old was Mary’s father when he was 4 times as old as Mary?
Means that I am looking for y when y=4x
So I go back to the equation: y-x=30
4x-x=30
3x=30
x=10
So y= 30 + x= 40

Question b) In how many years’ time will her father be 3 times as old as Mary?
So here y=3x
Here we go again: y-x=30
3x-x=30
2x=30
x=15
So y=45
As Dad is now 42, that will be in three years.

Question 3) cf yoyo

But I add my voice to sherry’s to ask for details about worksheets in this matter...
Jane

[sherry_d]

Thanks Jane thats really helpful the way you explained it.

[JaneEyre]

Well, I love algebra, but I hate percentages... So it's my turn to ask a question
This exercise comes from Bond - How to do 11+ maths, ex 7 page 46:

If there are 400 books in a library and 160 of them are fiction, what percentage of them is non fiction?

I manage to find the correct answer but I am wondering if there is a quicker way...


Here is how I did it:
number of non-fiction books: 400-160= 240

I know that 10% of 400 is 40.
240 is 40x 6
so the answer is 60%

As you can see, I am doing some 'cooking in my pot' to find the answer

I am wondering if we coudln't just simply say:
The number of fiction books related to the total number in the library is
240/400= 60/100=60%
That's far quicker

[yoyo123]

yes, that;'s ok.

or 160/400 = 40/100 = 40% fiction so 60% non-fiction

[mystery]

Going back to the OP, it's possible to get a v. high score and not answer the algebra questions in the Kent test isn't it?