# Thread: Algebra problem involving standard notation & %.

1. ## Algebra problem involving standard notation & %.

The human body can produce 2.5 million blood cells per second. If a person donates 500mL of blood, how long will it take to replace the red blood cells if a litre of blood contains 5 * (10^12) red blood cells?

The Sun is approximately 1.5 * (10^8) km from Earth and a comet is approximately 3 * (10^6) km from Earth. How many times further from Earth than the comet is the Sun?

A music store sells three types of CDs: classical, blues and heavy metal. In one week the sold a total of 420 CDs. They sold 10% more classical than blues whiles sales of heavy metal constituted 50% more than the combined sales of classical and blues CDs. How many of each type of CD did they sell?

2. Originally Posted by delicate_tears

A music store sells three types of CDs: classical, blues and heavy metal. In one week the sold a total of 420 CDs. They sold 10% more classical than blues whiles sales of heavy metal constituted 50% more than the combined sales of classical and blues CDs. How many of each type of CD did they sell

[I]
let x be classical
Blues: 0.10x+x
Classical and blues:0.10+2x
heavy metals: 0.5(0.10+2x)+(0.10+2x)= 3.15x

$\displaystyle x+0.10x+x+0.5(0.10+2x)+(0.10+2x)= 420$

$\displaystyle 2.1x+3.15x=420$

$\displaystyle 5.25x=420$

$\displaystyle x=80$

classical= 80
Blues= 0.10(80)+80 =88
heavy metals= 3.15(80)=252

$\displaystyle 80+88+252=420$

3. Originally Posted by delicate_tears

The human body can produce 2.5 million blood cells per second. If a person donates 500mL of blood, how long will it take to replace the red blood cells if a litre of blood contains 5 * (10^12) red blood cells?
$\displaystyle \frac{5*10^{12}}{2}=2.5*10^{12}$

$\displaystyle \frac{2.5*10^{12}}{2500000}=10000$seconds

$\displaystyle 10000 s * \frac{1min}{60s}$

$\displaystyle 166.66 hrs$

4. Originally Posted by delicate_tears
[snip]
The Sun is approximately 1.5 * (10^8) km from Earth and a comet is approximately 3 * (10^6) km from Earth. How many times further from Earth than the comet is the Sun?

[snip]
$\displaystyle \frac{1.5 \cdot 10^8}{3 \cdot 10^6}$ and the simplification should be straightforward.