Question

y
is inversely proportional to
x
.
When
y
=
9
,
x
=
8

Work out
y
when
x
=
4

Answer 1

$y \alpha \frac{1}{x} \\ y = \frac{k}{x} \: \: < where \: k \: is \: \: constant > \\ = > if \: \: y = 9 \: \: \: and \: \: \: x = 8 \: \: \: then \: k = xy \: means \: 9 \times 8 = 72$

$if \: \: \: x = 4 \: them \: \\ y = \frac{k}{x} \\ = > y = \frac{72}{4} \\ = > y = 18$