Y is inversely proportional to
x
.
When
y
=
25
,
x
=
4

Work out
x
when
y
=
20

x = 5

Step-by-step explanation:

Given that y is inversely proportional to x then the equation relating them is

y = ← k is the constant of proportion

To find k use the condition when y = 25 , x = 4 , then

25 = ( multiply both sides by 4 )

100 = k

y = ← equation of proportion

When y = 20, then

20 = ( multiply both sides by x )

20x = 100 ( divide both sides by 20 )

x = 5

you didn't post any answer choices, so its not 100% clear what your teacher is looking for

however, log(15/7) is equivalent to log(15) - log(7)

i'm using the rule log(x/y) = log(x) - log(y)