Thread: Here's another question on finding X

1. Here's another question on finding X

Is there a trick to finding the value of X?

Example:
75% of x = 1050
90% of x = 1260

I know that x = 1400, but I'm wondering if there's an easy way to find it out quickly.

Thx!

2. Originally Posted by matoau
Is there a trick to finding the value of X?

Example:
75% of x = 1050
90% of x = 1260

I know that x = 1400, but I'm wondering if there's an easy way to find it out quickly.

Thx!
of = "Multiply" $75 \%=\frac{3}{4} \mbox{ and }90 \%=\frac{9}{10}$

so solving each equation gives.

$\frac{3}{4}x=1050 \iff x=\frac{4}{3}1050=4 \cdot 350=1400$

and the second

$\frac{9}{10}x=1260 \iff x =\frac{10}{9}1260=10 \cdot 140=1400$

Fractions can make calculations alot easier.

I hope this helps.

3. Yes Yes Yes!

4. actually, i'm confused (again) at this part:
$
x=\frac{4}{3}1050=4 \cdot 350=1400
$

how does this give us 4? and why is the 4 and 3 flipped? division?
$
x=\frac{4}{3}1050=4
$

also, where does this come from?
$
4 \cdot 350
$

yeah, so where does the the 350 and 140 come from? how is it derived?

5. $\frac{3}{4}x=1050$ so we divide both sides by 3/4

$\frac{\frac{3}{4}x}{\frac{3}{4}}=\frac{1050}{\frac {3}{4}}$

remember that 1050 can be written as a fraction $\frac{1050}{1}$

and if we have a fraction divided by a fraction it is the same as multiplying by the reciprocial.

So now we get...

$x=\frac{\frac{1050}{1}}{\frac{3}{4}}=\underbrace{\ frac{1050}{1}\cdot \frac{4}{3}}_{1050/3=350}=350 \cdot 4=1400$

I hope this clears it up

6. Yes, thank you...

7. hi

Just divide 1260 with 0,9.

1260/0.9 = 1400

8. Originally Posted by Twig
Just divide 1260 with 0,9.

1260/0.9 = 1400
Fractions > Decimals
Originally Posted by TheEmptySet
$\frac{3}{4}x=1050$ so we divide both sides by 3/4

$\frac{\frac{3}{4}x}{\frac{3}{4}}=\frac{1050}{\frac {3}{4}}$

remember that 1050 can be written as a fraction $\frac{1050}{1}$

and if we have a fraction divided by a fraction it is the same as multiplying by the reciprocial.

So now we get...

$x=\frac{\frac{1050}{1}}{\frac{3}{4}}=\underbrace{\ frac{1050}{1}\cdot \frac{4}{3}}_{1050/3=350}=350 \cdot 4=1400$

I hope this clears it up
Nice Latex