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Q1:

#!/usr/bin/perl -w

$radius = 12.5;
$pi = 3.141592654;
$circumference = 2 * $pi * $radius;
print "The circumference of a circle with a radius of $radius is $circumference.\n";

exit;

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Q2:

#!/usr/bin/perl -w

$pi = 3.141592654;

print "Type in the radius of a circle and I'll calculate the\n";
print "circle's circumference.\n";
print "Type in a number and press ENTER.\n";
chop( $radius = <STDIN> );
$circumference = 2 * $pi * $radius;
print "The circumference of a circle with a radius of $radius is $circumference.\n";

exit;

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Q3:

#!/usr/bin/perl -w

print "Give me two numbers and I'll multiply them.\n";
print "Type in the first number and press ENTER.\n";
chop( $firstNum = <STDIN> );
print "Type in the second number and press ENTER.\n";
chop( $secondNum = <STDIN> );
print "$firstNum times $secondNum is ",$firstNum*$secondNum,".\n";

exit;

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Q4:

#!/usr/bin/perl -w

print "Give me a string and I'll print it out a bunch of times.\n";
print "Type in your string and press ENTER.\n";
chop( $str = <STDIN> );
print "Type in the number of times to repeat the string and press ENTER.\n";
chop( $repeat = <STDIN> );
print "$str\n" x $repeat;

exit;