Question

joel has twice as many CDs as Mariella has. subtracting 7 from the number of cds joel has and dividing by 3 equals the number of cds Blake has. If blake has 25 cds, how many cds does Mariella have?

Answer 1

We can write each of the statements as an equation

1. Joel j has twice the number of CDs as Mariella m, hence

j=2m

2. Joel's number of CD's - 7 divided by 3 equals the number of CDs Blake b has:

28j-729 2F3=b

3. Blake has 25 CDs

b=25

Substituting (3) into (2) gives:

%28j-7%29%2F3=25

j-7=3x25

j-7=75

j=75%2B7

j=82

So Joel has got 82 CD's

Based on equation (1) we can calculate the number of CD's Mariella has:

82=2m

m=82%2F2

m=41

Mariella has 41 CDs

Joel has 82 CDs

Blake has 25 CDs

Answer 2

j = number of cd's joel has
m = number of cd's mariella has
b = number of cd's blake has

from problem statement, develop equations:
j = 2m
b = (j - 7)/3 = 25
m = ?

solve for m

b = 25 = (j - 7)/3
25 = (j - 7)/3
25*3 = j - 7
75 + 7 = j
j = 82

j = 2m = 82
m = 82/2
m = 41

thus
mariella has 41 cd's
joel has 82 cd's
blake has 25 cd's