Answer:
 Length of one string is 7 cm less than the length of second string. OR Length of second string is 7 cm longer than length of one string.
Explanation:
Given : lengths of two strings are 10 centimeters and 17 centimeters. 
To find : Describe how the lengths of these two strings compare.
Solution : We have given that
 Length of one string =10 cm.
Length of second string = 17 cm
We can compare both length in many way 
Length of one string is 7 cm less than the length of second string.
OR
Length of second string is 7 cm longer than length of one string.
Therefore, Length of one string is 7 cm less than the length of second string. OR Length of second string is 7 cm longer than length of one string.