Hey there!!
Let's write $1.5 as 15 / 10
15/10 = 3/2
$3/2
October price = $3/2
Let's take September price as ' x '
If we take a look at the question, we know
October price = 20% of September + September price
20% = 20/100 = 1/5
Of = multiplication
Plug in the values
3/2 = x/5 + x
LCM = 5
3/2 = 6x / 5
Multiplying by 5 on both sides
15/2 = 6x
Dividing by 6 on both sides
15/2 / ( 6 ) = x
15/2 × 1/6 = x
15/12 = x
15/12 = $1.25
The price in September = $1.25
Hope my answer helps!