Question

The ratio of the prices of Emma's phone to Sophie's phone is 7:8. If Sophie's phone costs $640, how much should the prices of their phones decrease in order to have a ratio of 9:11 ?

Answer 1

Let cost of Emma's phone = x

Given that cost of Sophie's phone = 640

Then ratio of their phones cost will be x:640 or x/640

Given that ratio of their phones cost is 7:8 or 7/8

So both ratios will be equal.

$\frac{x}{640}=\frac{7}{8}$

$x=\frac{7}{8}*640$

x=560

So the new ratio of the cost of their phones will be 560:640

Now we have to find about how much should the prices of their phones decrease in order to have a ratio of 9:11.

So let that decreased amount is k then we will get equation :

$\frac{560-k}{640-k}=\frac{9}{11}$

11(560-k)=9(640-k)

6160-11k=5760-9k

6160-5760=11k-9k

400=2k

200=k

Hence final answer is prices of their phones should decrease by 200 in order to have a ratio of 9:11.