3-columns

3x + 2g = 700
g stands for gap.

#featured-post-6 article {
	width: 31.428571428571%; /* value of x  */
}

#featured-post-6 article:nth-of-type(3n+1),
#featured-post-6 article:nth-of-type(3n+2) {
	float: left;
	margin-right: 2.857142857143%; /* value of g */
}

#featured-post-6 article:nth-of-type(3n+0) {
	float: right;
}

4-columns

4x+3g = 880
Let's say g = 20px
x = 205

.below-home-featured .entry {
	border-bottom: none;
	width: 23.2954545455%;
}

.below-home-featured .entry:nth-of-type(4n+1),
.below-home-featured .entry:nth-of-type(4n+2),
.below-home-featured .entry:nth-of-type(4n+3) {
	float: left;
	margin-right: 2.2727272727%;
}

.below-home-featured .entry:nth-of-type(4n+0) {
	float: right;
}

4n+0: 0, 4, 8...
4n+1: 1, 5, 9, 14...
4n+2: 2, 6, 10...
4n+3: 3, 7, 11...