Two like magnetic poles of strength 10 and 40 SI units are separated by a distance 30 cm. The intensity of magnetic field is zero on the line joining them

Suppose magnetic field is zero at point P which lies at a distance x from 10 units pole. Hence, at Pμ04π.10x2=μ04π.4030-x2⇒x=10 cmSo, from stronger pole distance is 20 cm.