To do these problems think of four boxes, where each box represents a digit.
In the first box, you can only have 1-9, excluding 7 (1, 2, 3, 4, 5, 6, 8, 9), that's 8 numbers. Basically, it's the same as the next three boxes, except zero is also excluded.
In the second, third, and forth boxes, you can have 0-9, excluding 7, which is 9 numbers.
To find the answer, multiply the possibilities by each other.
"Box 1" x "Box 2" x "Box 3" x "Box 4"
8 x 9 x 9 x 9 = 81 x 72 = 5832 possibilities
The answer is 5832 possibilities.
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From 1000 to 9999 (inclusive) there are 9999 - 1000 + 1 = 9000 integers. Half of which are even, half of which are odd. So the answer is 9000/2 = 4,500.
9000 integers.
To find the number of even integers between 100 and 1000, we first determine the number of even integers between 1 and 1000, which is half of the total integers (since every other integer is even). So, 1000/2 = 500 even integers between 1 and 1000. Next, we subtract the number of even integers between 1 and 100, which is 50 (since every other integer is even in this range as well). Therefore, there are 500 - 50 = 450 even integers between 100 and 1000.
31.how do you solve?
128!