The following describes a procedure to determine whether a number is divisible by 7. We will demonstrate the procedure with the number 203.

(i) Remove the units digit from the number, double the units digit, and subtract it from the remaining number. For 203, we will remove the 3, double it to get 6, and then subtract 20 - 6 to get 14.

(ii) If this new number is divisible by 7, then so is the original number. In our case, since 14 is divisible by 7, then 203 is also divisible by 7.

(iii) If you are not sure if the new number obtained in Step ii is divisible by 7, you can repeat the process described in the first step.

Use the procedure described above to determine whether the following numbers are divisible by 7.

(a) 329

(b) 553

(c) 583

(d) 4823