FSMQ HELP!! velocity equation/simplifying equations question

Really stuck on this question:

june 2008 OCR FSMQ paper

q10, (ii)

explain why 140/v - 140/v+5 = 1/4 and show that this equation reduces to the equation v^2 + 5v - 2800 = 0

i understand the first part (explain why it is equal to one quarter) but how does the first equation reduce to the second one?!!!!!

any help would be much appreciated ☺️☺️☺️

Reply 1

Zen-Ali

Original post by madisonyoung

...

Try and get rid of the denominators that have

v, v + 5

in them. With some manipulation, you should get to the correct answer.

Reply 2

madisonyoung

Original post by Zen-Ali

Try and get rid of the denominators that have

v, v + 5

in them. With some manipulation, you should get to the correct answer.

I'm trying but I have no idea how to work fractions.. Do you have any tips for this?

Reply 3

Zen-Ali

Original post by madisonyoung

...

I just checked now and I got the correct answer. Usually with algebraic fractions such as these it is quicker to multiply through by a number that will quickly cancel all denominators, but to explain how it works to you/to let you see it for yourself, multiply both sides of the equation by

4

, then by

v + 5

and then by

v

. If you rearrange the expression you get, you should get to the answer.

Reply 4

davros

Original post by madisonyoung

I'm trying but I have no idea how to work fractions.. Do you have any tips for this?

You need to show some working if you're still stuck.

Manipulating algebraic fractions is no different from manipulating numeric fractions at the end of the day.