$durations: ( 250, 500, 1000, 1500, 2000 );

.trn {
    @each $value in $durations {
        &\:#{$value} {
            transition: #{$value}ms ease;
        }
    }
    @each $value in $durations {
        &-dly\:#{$value} {
            transition-delay: #{$value}ms;
        }
    }
}