To find all common multiples of two numbers, you first need to split them into their prime factors:
21 = 3x7
14 = 2x7
The next step is to identify any common factors. In this case, both numbers have 7 as a factor so we can discard one 7. Take every other prime factor (2, 3 and 7) and multiply them together to get the LCM:
2x3x7=42
To find any other common multiple, you simply multiply this number by an integer (2,3,4...). By doing this, you find that the first few numbers that 21 and 14 both go into are:
42, 84, 126, 168...
42
7
The number 7
14, remainder 5
Numbers that can go into 42 are 1, 2, 3, 6, 7, 14, 21, and 42.
14. If you have the numbers in order like so: 7,9,11,14,21 you can see that 21 is the greater number. You then subtract 21 from the smallest number, 7, and you get 14.
308 ÷ 21 = 14 with remainder 14
7
21
The answer is 1414
21 divided by 14 equals 1 with a remainder of 7.
The answer is 7. The equation is x+14=21, so you would find x by doing 21-14=7 x=7
Any number between 21 and 14 can be an arithmetic mean.