## 20 Feb Tuesday 7:30 Python Practice – 22.02.15.

**Question:**

The International Standard Book Number (ISBN) is a 13-digit code for identifying books. These numbers have a special property for detecting whether the number was written correctly.

The 1-3-sum of a 13-digit number is calculated by multiplying the digits alternately by 1’s and 3’s (see example) and then adding the results. For example, to compute the 1-3-sum of the number 9780921418948 we add

9 ∗ 1 + 7 ∗ 3 + 8 ∗ 1 + 0 ∗ 3 + 9 ∗ 1 + 2 ∗ 3 + 1 ∗ 1 + 4 ∗ 3 + 1 ∗ 1 + 8 ∗ 3 + 9 ∗ 1 + 4 ∗ 3 + 8 ∗ 1

to get 120.

The special property of an ISBN number is that its 1-3-sum is always a multiple of 10.

Write a program to compute the 1-3-sum of a 13-digit number. Your program should input a 13-digit number and then print its 1-3-sum. Use a format similar to the samples below.

Sample Interactive Session 19780921418948Output for Sample Interactive Session 1The 1-3-sum is 120

Sample Interactive Session 29780921418052Output for Sample Interactive Session 2The 1-3-sum is 108

Hint:1. You could use input() to ask user enter 13-digit number. However, remember the information you entered will be a string if you only use input() 2. if you use variable name calledto assign with input information, then you should use for loop like below to get every character from digits. for c in digits: 3. You should always use int() to convert every single character into integer numberdigits

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