if a book costs $5 and the new price is $6, then if a book costs $100 what is the new price?

Question

My father said,
A book costing $5, raised to $6 has a 1 dollar increment.
Therefore every $5= +1
There are 20 ($5) in $100. So 20(1) + 100 = 120

I don't get this.
What does it mean.
If a book costs $4 dollars, its new price is $5 dollars.
If a book cost $128 dollars, what is its new price.
[Shouldn't new price be 129 dollars?]

Is this true? What is my father saying????????????

Answer 1

If a book costing 5$ raises to 6$, it had a 20% increase. Therefore you must find 20% of 100$ and add it to the 100$. Since 20%of 100$ is 20%,
20 + 100 = 120
Hence, you would pay 120$.
______________________________

If a book origianally costing 4$ was raised to 5$, it had a 25% increase. :

4 ---128
-- = ----
5 -----x

Now, use cross multiplication.

4x = 5 X 128

4x = 640

4x/4 = 640/4

x = 160

So you would pay 160$ instead of 128$.

Answer 2

Well I think some people already answer it but you may still be confused. This question test your division, multiplication, addition, and subtraction skills. It also ask how much would the increase be from the original price? Then again, are these the same book?

I think you know how to solve the problem; however, I see what you mean. If there's a $1 difference between $5 and $6 then why is the new price $120 instead of $101.

You're basically trying to figure out how much to increase the cost of the new book based on the first ($5) and second price of the book ($6). When you get the difference, you are trying to find out how many $5 would go into the third price ($100). That way you can figure out your price increase. The $20 is the price increase here and you have to add that with $100 in order to get the new price.

If the book cost $5 and then $7, there's a $2 difference. How many $2 goes into $100? It would be a $50 increase (100 divide by 2 = 50). So if there's a $50 increase you would have to add $100 to that and get $150 for the new cost.

Good question though. Had me thinking too.

Answer 3

It is true it is $120 not $101 because an increase of $1 for the $5 book is an increase of 20% so an increase of 20% to $100 is of course $20 it works the same way for the $4 and $128 and it can not be $129 unless it is the same % for the $4.

Answer 4

A book costing $5, raised to $6 has been increased in price by 20% (which is a 1 dollar increment).
A book costing $100 + 20% = $120
If a book costs $4 dollars, its new price is $5 dollars.
The increase here is 25%.
You can finish it from here.

Answer 5

If a book is $128... the new price would be 160 wouldn't it? 128/4=32 128+32=160

Answer 6

You have it right in the first paragraph, it is a proportion.

Try an equation like: oldprice/newprice = oldprice/newprice
e.g.
4/5 = 128/x

then solve for x

Answer 7

Wait, are you in COLLEGE and asking this?

Follow the same principle as in the first example.

x=original cost=4 in this case
x+1=new price=5
128/4=32=number of books(using old pricing)
32*(x+1)=32*5=$160

Answer 8

it is a ratio, think of it as fractions 5/6 = 100/x cross multiply and you get 600=5x, x=120
4/5 = 128/x, 4x = 640, x = 160

Answer 9

I would set up a cross multiplication problem....


5 100
_ = ____
6 ?

multiply 6 x 100 then divide by 5 and you will have your answer.

Answer 10

the top answer is $120.00. which is a 20% increase
your bottom question is $160.00 which is 25% increase