# Math Help - problem solving need helpp

1. ## problem solving need helpp

heys, i finished a whole chapter but got stuck on these questions

1.The human body can produce 2.5 million blood cells per second. If a person donates 500 mL 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?

2.The Sun is approximately 1.5 × 108 km from Earth and a comet is approximately
3 × 106 km from Earth. How many times further from Earth than the comet is the Sun?

thks

2. 1.The human body can produce 2.5 million blood cells per second. If a person donates 500 mL 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 man has donated 500ml of Blood
so he has donated
$\frac{5\times 10^{12}}{2}$ blood cells

Which he needs to recover at the rate of 2.5 x 10^6 blood cells per second

Hence lets say it takes n seconds to do so
so
$(2.5 \times 10^{6}) \times n = 2.5 \times 10^{12}$

Hence n = 10^6 second = 10,00,000 second

2.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?

Distance of sun from comet = 1.5 \times 10^8

Distance of sun from earth = 3 \times 10^6

it will be given by

$\frac{ 1.5 \times 10^8}{ 3 \times 10^6}$

$
=\frac{ 1.5 \times 10^{8-6}}{ 2 \times 1.5}$

$
=\frac{ 10^{2}}{ 2 }$

$=\frac{ 100}{ 2 }$

$=50$
Thus it is 50 times the distance of sun and earth

3. hey thanks so much,

this question is doing my head in.

A music store specialises in three types of CDs: classical, blues and heavy metal. In oneweek they sold a total of 420 CDs. They sold 10% more classical than blues while 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?

LET:
classical=c
blues=b
heavy metal=h

1/10c+b
1/2h =(c+b) ???? not sure of the equations

4. Originally Posted by smmmc
hey thanks so much,

this question is doing my head in.

A music store specialises in three types of CDs: classical, blues and heavy metal. In oneweek they sold a total of 420 CDs. They sold 10% more classical than blues while 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?

LET:
classical=c
blues=b
heavy metal=h

1/10c+b
1/2h =(c+b) ???? not sure of the equations
Well heavy metal would make up 2/3 of the sales because it's 50% more not just 50%. So heavy metal would be 280 CDs. As for blues and classical, it's 2:45 in the morning haha if there's no response I'll work on it tomorrow.

5. Please disregard my first post haha. Heavy metal equals 252 and the other two equal 168. Half of 168 added onto 168 will get you 252. Classical equals 88 and Blues equals 80. Again it was another guess and check but 80 multiplied by 10% will give you 8 and 80 plus 88 will give you 168. If you're looking for an equation I don't have it but those are the answers.

6. LET:
classical=c
blues=b
heavy metal=h

1/10c+b
1/2h =(c+b) ???? not sure of the equations

First of all
Its always better if you start new questions in new threads

LET:
classical=c
blues=b
heavy metal=h

$c+b+h= 420.................(1)$

$c= \frac{110}{100}\times b.................(2)$

$
h= \frac{150}{100}\times(b+c)= \frac{15}{10}\times(b+\frac{11b}{10})............. ...........(3)$

Put 2 and 3 in (1)

$\frac{21\times 15}{10 \times 10}b+ \frac{11b}{10} + b= 420$