installing php-mbstring for Facebook php sdk on Centos 7

I have run this command

sudo yum install php-mbstring

but I got this error

Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirrors.tripadvisor.com
 * epel: mirror.cogentco.com
 * extras: mirror.solarvps.com
 * remi-safe: mirrors.mediatemple.net
 * updates: mirror.solarvps.com
 * webtatic: us-east.repo.webtatic.com
No package php-mbstringyum available.
No package install available.
Resolving Dependencies
--> Running transaction check
---> Package php-mbstring.x86_64 0:5.4.16-36.el7_1 will be installed
--> Processing Dependency: php-common(x86-64) = 5.4.16-36.el7_1 for package: php-mbstring-5.4.16-36.el7_1.x86_64
--> Running transaction check
---> Package php-common.x86_64 0:5.4.16-36.el7_1 will be installed
--> Processing Conflict: php70w-common-7.0.2-1.w7.x86_64 conflicts php-common < 5.5.0
--> Finished Dependency Resolution
Error: php70w-common conflicts with php-common-5.4.16-36.el7_1.x86_64
 You could try using --skip-broken to work around the problem
 You could try running: rpm -Va --nofiles --nodigest

what should I do to fix and install php-mbstring ?

Solution

You've installed PHP 7 [phpw70] from a custom repo. [webtatic]
You're trying to install a 5.4 package [php-mbstring] from CentOS base, so:
```
Error: php70w-common conflicts with php-common-5.4.16-36.el7_1.x86_64
```

Which is precisely why all [decent] custom repos use non-standard package names, so as not to conflict with base and install random, conflicting versions.

yum list php70w*
Find the package you want.
yum install $package