# Talk

## Help algebra!

(20 Posts)
Mandzi34 Wed 02-Nov-16 21:56:56

Can someone help me with the following:

A father is 24 years older than his daughter (is now)

Two years ago he was four times as old as his daughter (was then)

If you let the daughter's age (now) be d:

By reading the second sentence (in the question) again use terms of d, to find how old the daughter is now.

I believe she's 10 but am having trouble isolating d to find the answer? Am I completely off?

Trying to teach myself to help DS.

irvineoneohone Wed 02-Nov-16 22:04:09

F = d +24
F-2 = (d-2)4
d+24-2 = 4d-8
d+22=4d-8
3d=30
d =10?

Mandzi34 Wed 02-Nov-16 22:07:09

Thanks Irvine. Do you believe the 10 is right?

PurpleDaisies Wed 02-Nov-16 22:08:07

irvine is spot on...I wonder if you missed that the first sentence also needed to be turned into an equation and then you can solve them as simultaneous equations? The way the question is worded it sounds like you only need to use the second sentence.

poohbear123 Wed 02-Nov-16 22:10:25

If f is father's age now, and d is daughter's age now:

We know:
Firstly d = f - 24
Secondly f - 2 = 4 x (d - 2)

rearranging the second:
f = 4d - 8 + 2
f = 4d - 6

Substituting f into the first:
d = 4d - 6 - 24
d = 4d - 30
-3d = -30
d = 10

Wed 02-Nov-16 22:37:38

Turn sentence 1 into an equation:
F= d + 24

Sentence 2 relates to 2 years ago (so "-2"):
F-2=4×(d-2)
F-2=4d - 8

Then rearrange it so that you have only the F on the left:
F=4d -8 + 2
F=4d -6.

Now you have two equations that both equal 'F'.

d + 24 = 4d -6

Rearrange so that all the letters are on one side and numbers on the other:
24 = 4d -6 -d
24 = 3d -6
24 +6 =3d
30 = 3d
d=10

Mandzi34 Thu 03-Nov-16 14:17:41

Thanks all!

pasanda Fri 04-Nov-16 21:42:45

Bloody hell! My head hurts reading that.....!

Pythonesque Wed 09-Nov-16 07:17:29

When you want to check an answer with a question like this, it is usually easier than working it out in the first place. Just go back to the start and say, if the daughter is 10 now then the father is 10+24 = 34 now. Two years ago he was 34 -2 = 32 years which is 4 x 8. Two years ago his daughter was indeed 10 - 2 = 8 years so you know you are right.

Mandzi34 Wed 09-Nov-16 20:59:28

I am trying to teach DS how to use algebra like the question above. I found a question in his book which wasn't asking for algebra but I was hoping someone could help me work it out using algebra?

My daughter asked how old I am. I answered 'In 20 years, I'll be twice as old as I was 12 years ago. How old am I'?

So if I used X, how can I find the answer?

irvineoneohone Wed 09-Nov-16 21:51:29

x+20 = 2(x-12)
x+20 = 2x-24
20+24 = 2x-x
x= 44

irvineoneohone Wed 09-Nov-16 21:59:18
irvineoneohone Wed 09-Nov-16 22:02:16
irvineoneohone Wed 09-Nov-16 22:07:14
Mandzi34 Wed 09-Nov-16 22:21:09

Thank you very much! That really helps. I'm going to try and do lots of practice!

irvineoneohone Thu 10-Nov-16 06:10:28

Forgot to add, as Pythonesque suggests, you can substitute x with your answer and check if your answer is correct.

44+20 =64
2(44-12) = 2 x 32 = 64

I am learning maths to help my ds as well. Khanacademy really helped me.

Mandzi34 Thu 10-Nov-16 11:40:45

Thanks all.

irvineoneohone - you are brilliant! Your DS should be very grateful. I still struggle with what to do with X etc.

irvineoneohone Thu 10-Nov-16 12:31:04

This might help as well.

uk.ixl.com/search?q=write+a+equation

It is a paid site, but you are allowed to practice up to about 20 question for free.

irvineoneohone Thu 10-Nov-16 12:33:21

"you are allowed to practice up to about 20 question for free a day."

Mandzi34 Thu 10-Nov-16 14:41:52

Thanks! I've used that site before. It is a good one.

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