1. Riana has been asked to erase digits from the number 12323314 to obtain a number which reads the same from left to right as it does from right to left. What is the smallest number of digits Riana needs to erase?
A 1
B 2
C 3
D 4
E 5
1. C The only digit 4 is at the end of the number and hence to obtain a number which reads the same from left to right as it does from right to left (known as a palindromic number), the first step is to erase the 4 leaving the number 1232331 . There are now three different possibilities to produce a palindromic number - erasing the two 2 s to leave 13331 , erasing the final two 3 s to obtain 12321 or erasing the first 2 and the either the last or second last 3 to obtain 13231 . However, in each case three digits have been erased.