Calculation using expr in shell

Question

I have used the following code to Calculate simple intrest and its working fine

intrest=$(( $p * $r * $t / 100 ))

However when i try to solve the above using expr it gives me error expr: syntax error

intrest=`expr $p * $r * $t / 100`

Answer 1

You need to escape the *s.

intrest=`expr $p \* $r \* $t /100`

This has nothing to do with more than two variables.

intrest=`expr $p * $r`

doesn't work either.