Find the least square number which is exactly divisible by 10,12,15 and 18.

       L.C.M. of 10, 12, 15, 18 = 180. Now, 180 = 2 * 2 * 3 * 3 *5 = 2² * 3² * 5.

       To make it a perfect square, it must be multiplied by 5.

        Required number = (2² * 3² * 5²) = 900.