all two-digit numbers whose units digits is half the tens digit?
Odd numbers cannot be used in the tens digit.
84, 63, 42, 21
To find all two-digit numbers whose unit digit is half the tens digit, we can break down the problem into two parts.
First, we need to determine the range of possible tens digits. Since the tens digit cannot be zero (as the number needs to be two digits), we can start from 1 and go up to 9.
Next, for each tens digit, we can determine the possible unit digits that satisfy the condition of being half the tens digit. For example, if the tens digit is 1, the possible unit digits would be 0 (half of 0 is 0) and 5 (half of 1 is 0.5, but since it needs to be a whole number, we take the closest lower whole number, which is 0).
Following this approach, we can iterate through all possible tens digits (1 to 9) and find the corresponding unit digits that satisfy the condition.
Let's list the two-digit numbers where the unit digit is half the tens digit:
10 (1 x 5 = 5)
12 (1 x 6 = 6)
14 (1 x 7 = 7)
16 (1 x 8 = 8)
18 (1 x 9 = 9)
20 (2 x 0 = 0)
24 (2 x 4 = 8)
28 (2 x 8 = 16, rounded to 8)
30 (3 x 0 = 0)
32 (3 x 2 = 6)
36 (3 x 6 = 18, rounded to 8)
40 (4 x 0 = 0)
42 (4 x 2 = 8)
48 (4 x 8 = 32, rounded to 2)
50 (5 x 0 = 0)
54 (5 x 4 = 20, rounded to 0)
60 (6 x 0 = 0)
64 (6 x 4 = 24)
70 (7 x 0 = 0)
72 (7 x 2 = 14, rounded to 4)
80 (8 x 0 = 0)
90 (9 x 0 = 0)
Therefore, the two-digit numbers whose unit digit is half the tens digit are: 10, 12, 14, 16, 18, 20, 24, 28, 30, 32, 36, 40, 42, 48, 50, 54, 60, 64, 70, 72, 80, and 90.