If the interpreter implemented the interpolation you are specifying, then how could I as a programmer make it output the string Product is 5 * 3? There'd be some pretty non-intuitive side effects.
Kenosis below has given you a way to be clever, but this is all getting a little clever for my taste. For complex output, I usually prefer going all the way to printf since, after all, you desire a formatted print. So maybe printf "number is %d\n", $number * $multiplier;. toolic's solution still strikes me as pretty clean as well.
#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.