Kenneth spent 10% of this earnings this week on a new joystick. If he is left with $405, how much were his earnings? Let's think first. Chain of thought:
Since Kenneth spent 10%, then he is left with 100% - 10% = 90% of his earnings. Since 90% of his earnings is worth $405, then 1% of his earnings is $405 / 90 = $4.50. Hence, Kenneth's earnings is $4.50 x 100 = $450.
Therefore, the answer is 450.