Fun With 5's - 2

So, what happens when the numbers are not the same, but they are only 10 apart. For example, 55x65. These solutions are just as simple, only a little different. In these cases, the answer will end with “75” instead of “25”. You will still be multiplying the first numbers, no manipulations necessary, but you need to add a number back in. That number will be the lower of the two front numbers. So, in our example of 55x65, you take the “5” from the 55 and the “6” from the 65, plus the same “5” from the 55. It would look like this: 5x6+5 (35). Then you add the “75” to the end. That gives you the answer of 3575. The problem of 85x75 would be 8x7+7 (63), then the “75”, so that makes 6375. Now figure out what 35x25 would be?

Now let’s move on to what to do if the numbers are further apart. For example, how would you handle 45x65? These are easy also, but I need to introduce something new to you here.

In these cases, ALL numbers more than 10 apart, to determine what the last 2 numbers will be there is a very simply process. In our example case, just subtract 6-4 (the first digits of each number). If you get an even number, the last 2 digits will be “25” and if you get an odd number they will be “75”. Easy.

To get the first part of the answer is almost as simple. First, you do the normal multiplication, in this case, 4x6. When you get your answer (24) you add back in the number that is exactly in between the 4 and 6, which, of course, is 5. It will look like this: 4x6+5=29, then add on the “25” because 6-4 equals 2 (an even number). The answer for 45x65 is 2925. If it’s 95x75 it will be 9x7+8 (71) and add the “25” (9-7=2). The final answer is 7125. Naturally, if the numbers are only apart by 20, it will always be an even number on the end.
In my final part, part 3 we will check to see what happens when they are further apart and that “odd number” pops up.

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