Derek finally gets his own allowance. He puts $2 away in January, $4 away in February, $8 away in March, $16 away in April and follows this savings pattern through to December. How much money does he have to spare and save by December? Let's think first. Chain of thought:
Derek doubles his allowance savings each month, so in May, Derek has $16 * 2 = $32. In June, Derek has $32 * 2 = $64. In July, Derek has $64 * 2 = $128. In August, Derek has $128 * 2 = $256. In September, Derek has $256 * 2 = $512. In October, Derek has $512 * 2 = $1024. In November, Derek has $1024 * 2 = $2048. By December, Derek has $2048 * 2 = $4096 to save.
Therefore, the answer is 4096.