Cents no more

Johnny bought pencils for 35 cents each. Neither he nor the salesperson had small coins, just a whole € 1 coin. At least how many pencils did he have to buy to pay for the whole euros?

Final Answer:

n =  20

Step-by-step explanation:

$$\begin{gathered} 35=5\cdot 7 \\ 100=2^2\cdot 5^2 \\ LCM(35,100)=2^2\cdot 5^2\cdot 7=700 \\ n=LCM(35,100)/35=20 \end{gathered}$$

Try another example