Build a cron image from centos, the size icreased about 100M, What is the problem?

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I built an image from centos the Dockerfile looks like:
FROM centos:latest
RUN yum install -y cronie
… …
the centos image is about 196M, after install the cronie the size grows up to 298M. the cronie package is only about 2.2 M, why the image size increased 100M?