Algebra equation problems

Your first equation doesn't account for the fact that the daughter aged 4 years. It should be:

x+4 = 3*(x-20+4)

Oh, I just calculated it. Thanks!! It's right. The answer is 26.

I've got another question. Got about six of them that I don't really get, to be honest.

Jarred is saving up to buy a new CD player costing $275. He has saved $95 so far and plans to save $15 per week from now on. How long will it take Jarred to save enough money for the CD player?

How much more does he have to save?

At $15/week, how long will it take him to save that much?

He has to save $180 more. I'm clueless on this one. I'm not sure which one I should put x as.

Edit-- He needs twelve weeks to save up to $180, right? How do I write out the equation?

*looks around thread* Are you there?

Never mind.

I got another one...

A bicycle wheel travels 10 metres in 6 1/2 revolutions. Find the diameter of the wheel to the nearest cm.

Here's my equation...

Let the diameter be d

6 1/2 x Pi x d = 10

I'm not sure if that's right or not.

How do you work the answer on that last question? I tried, but got it wrong. Do you first multiply everything by 2 since it's an inverse from the fraction of 1/2?

The diameter can be found when you know the circumference of the wheel.

d * pi = Circumference

The circumference is the distance that the wheel travels in one revolution
We know that it travels 10 meters in 6,5 revoutions, so in one revolution it travels:

10meters / 6.5 revolutions = 1.54 m / revolution ( = circumference)

so: d * pi = 1.54 ------> d = 1.54 / pi

Oh, thanks. I think I got it now. I've got some more.

- Three years ago, my brother was twice as old as my sister. Now he is 12 years older than she is. How old is my sister now?

- A farmer raises pigs and emus. From a total of 42 animals, she counted 116 legs. Use the guess, check and improve method to find how many pigs the farmer has.

- A pay clerk orders a payroll in $20 and $50 notes. He needs 85 notes talling $2780. Use the guess, check and improve method to calculate how many $20 notes he much order.

- A cyclist takes five hours to complete a 94 km ride. She averages 15 km/h for some of the journey and 20 km/h for the rest. Use the guess, check and improve method to calculate the length of time she was travels at 15 km/h.

- A man is twice as old as his daughter; 10 years ago he was three times as old. How old is the daughter now?

- The number 57 is divided into two parts so that the sum of one-fifth of the first and one-sixth of the second is 10. What are the two parts?

- A container of water is 4/5 full. When 10 litres are taken out, the container is only 2/3 full. How many litres does the container hold?

The bolded ones are the ones I'm having major difficulty with. Can anyone please help?

First one--ask yourself what are the unknowns? It's you brothers and your sisters present age. Set some unknown quantity equal to your brother's age and your sister's age. Then reread the problem. "Three years ago", now that implies that when your brother and sister were three years younger than they are now (subtract 3 from your brother and sister's present ages); your brother was then twice as old as your sister was then.

Now I know my brother's present age is 12 more than my sister's present age.

Now I have two relationships between my brother's age and my sister's age. I can now use one relation to substitute one variable (say my brother's age) in terms of the other variable (my sister's age) into the other relationship and solve for a variable (in my selection, my sister's age). The other variable (brother's age) will then pop out of either relationship

The rest are solved similarly.

Rap

I did it like this...

Let sister's age be y



But that's wrong. I don't know what I'm doing wrong.

let y be your sisters age
three years ago your brother's age was twice as old as your sister
three years ago your brother age was y+12-3 and your sister's was y-3.

Rap

Let me check...



Awesome, that's right!! *hugs*