To find the percentage difference between two numbers, we first need to find the absolute difference between them. In this case, the absolute difference between 420 and 240 is 180 (420 - 240 = 180).

Next, we need to find the average of the two numbers. The average of 420 and 240 is (420 + 240) / 2 = 330.

Now, we can find the percentage difference by dividing the absolute difference by the average and multiplying by 100. So, the percentage difference between 420 and 240 is (180 / 330) x 100 = 54.55%.

This means that the second number (240) is 54.55% less than the first number (420). Alternatively, we can say that the first number (420) is 54.55% more than the second number (240).