PHP Random "Splited right and Left Side" background image

Guys im trying to implemnet a random background image for my site this works also fine but the problem is i have two different images which should be union for Example both backgrounds. i have 5 different background designs with on set (1 set = 2 images)one for the left and another for the right side. But they don't match anybody an Idea? Thanks!

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<div class="tak-bg tak-bg-left bg<?php echo rand(1, 5); ?>
<div class="tak-bg tak-bg-right bg<?php echo rand(1, 5); ?>

sass code