(x-21/7)+(x+4/4)=x-4

Question

turingtest · Answer

$${x-21\over7}+{x+4\over4}=x-4$$correct?

anonymous · Answer

yes

turingtest · Answer

find the common denominator between the 3 fractions

anonymous · Answer

i need help though

turingtest · Answer

do you know how to find the Least common multiple (LCM) of a set of numbers?

anonymous · Answer

i found the common denominator

turingtest · Answer

what is it?

anonymous · Answer

28

turingtest · Answer

right :)
now multiply everything (the *entire* equation) by that

anonymous · Answer

why do i multiply that to everything? i thought its supposed to be the denominator

turingtest · Answer

by finding the LCM of the denominators and multiplying the whole equation by that, you will find that all the fractions will disappear
it works like magic every time :)

anonymous · Answer

ohhh okay thanks ;)

turingtest · Answer

think of the LCM as $$28=7\cdot4=\frac{7\cdot4}1$$we multiply and things cancel$$\frac{\cancel 7\cdot4}1\frac{x-21}{\cancel 7}+\frac{7\cdot\cancel4}1\frac{x+4}{\cancel4}=\frac{7\cdot4}1(x-4)$$

turingtest · Answer

what is left is$$4(x-21)+7(x+4)=28(x-4)$$think you get the idea?

anonymous · Answer

indeed ;)

turingtest · Answer

I'm glad :)

anonymous · Answer

me too ... glad we met :)

turingtest · Answer

I'm glad you found OpenStudy
hope to see ya 'round !

anonymous · Answer

care to help me with another please?

turingtest · Answer

I have to go for a moment, sorry
also, please post each Q separately
thanks