PHP Fatal error:  Call to undefined function bcmul() in /php_rsa.php on line xxx

yum install php-bcmath

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Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package php-bcmath.x86_64 0:5.1.6-40.el5_9 set to be updated
--> Processing Dependency: php-common = 5.1.6-40.el5_9 for package: php-bcmath
--> Running transaction check
---> Package php-common.x86_64 0:5.1.6-40.el5_9 set to be updated
--> Processing Conflict: php53-common conflicts php-common
--> Finished Dependency Resolution
php53-common-5.3.3-13.el5_9.1.x86_64 from installed has depsolving problems
  --> php53-common conflicts with php-common
Error: php53-common conflicts with php-common
 You could try using --skip-broken to work around the problem
 You could try running: package-cleanup --problems
                        package-cleanup --dupes
                        rpm -Va --nofiles --nodigest

string bcmul ( string $left_operand , string $right_operand [, int $scale ] )

<?php
echo bcmul('1.34747474747', '35', 3); // 47.161
echo bcmul('2', '4'); // 8
?>

[bcmath]
; Number of decimal digits for all bcmath functions.
; http://www.php.net/manual/en/bc.configuration.php#ini.bcmath.scale
bcmath.scale = 0