NATIONAL MUTUAL CUTS AUSTRALIAN PRIME TO 17.75 PCT National Mutual Royal Bank Ltd said it would cut its prime rate to 17.75 pct from 18.25, effective April 27. The cut follows a trend toward lower rates started last month and accelerated by Westpac Banking Corp, which yesterday cut its prime to 17.50 pct from 18.25 pct. Westpac's 17.50 pct is the lowest prevailing rate.