Final answer:
To find out the new price per pencil, we converted the total bill into cents (21 cents) and divided it by the original price (6 cents), resulting in 3.5 pencils. Since half a pencil is not possible, it indicates that the price has increased. Therefore, the new price per pencil is 7 cents.
Step-by-step explanation:
The question asks how much the price of pencils has increased if originally each was 6 cents and the total bill came to $0.21. Firstly, we should convert dollars to cents to make it easier to calculate.
So $0.21 is the same as 21 cents.
To find out how many pencils were bought, we divided the total cost by the original price of one pencil.
Number of pencils = Total bill / Original price per pencil
Number of pencils = 21 cents / 6 cents per pencil = 3.5 pencils
Since we cannot have half a pencil in reality, it indicates that the price per pencil has risen. To find the new price, we divide the total bill by the actual number of pencils.
New price per pencil = Total bill / Number of pencils
New price per pencil = 21 cents / 3 pencils = 7 cents per pencil