Shell Programming and Scripting

Dear all,
I am new to shell scripting and have tried to make a small program for fun sake that tells age from the last number of cell phone and birth year.
At the end we get a final 3 digit number and the first digit represents the last digit of cell phone and rest 2 numbers shows age. eg. 423 ---> 4 being the last digit of the cell number and 23 is the age.
Now i want to format the answer in such a manner that i can filter out the first digit and only display the last two digits as age.
The following is the script:

Code:

#!/bin/bash
echo "enter the last digit of your mobile number: "
read num
echo "Enter your birth year in YYYY format: "
read byear
mult=`expr $num \* 2`
fift=`expr $mult + 5`
fifty=`expr $fift \* 50`
plus=`expr $fifty + 1763`
agex=`expr $plus - $byear`
echo "$agex ------>>>> the first digit of the answer is your last digit of your cell number and last two digits represents your age"

I would request forum members to help me on this... i have enjoyed this and want to explore more.
Thanks in advance.
stg44

Please use code tags as required by forum rules!

Using bash, did you consider the "parameter substring expansion" (man bash)?

Ok. will use code tags next time. will keep in mind.
as for the "parameter substring expansion" i am totally new to this so please bear my silliness.
i did the man bash but unable to get how to relate and manipulate.

${var:pos:len} will get you len characters of var, starting from pos. So

Code:

echo "${agex:1:2}"

https://www.gnu.org/software/bash/ma...Expansion.html

Thanks a lot Carlo M.
I appreciate that, and will go through the bash reference manual.