As in this case, pivalic acid is weak acid (Due to electron donating effect of <em>tert.</em> butyl group) having pka value of 5.0 , so its conjugate base will be strong as compare to formic acid which is stronger acid.
<em>Summary: </em>
As pivalic acid is weak acid as compare to formic acid, so its conjugate base will be strong and vice versa.