Question

What is the lcm of 4&14

12&21
16&12
25&30
40&50
18&24

Answer 1

Basically what you do is list the multiples of your given numbers, and the first number they have in common is your least common multiple.
1) 12: 12, 24, 36, 48, 60, 72, 84, 96, 108...
21: 21, 42, 63, 84, 105...
Answer: 84

2) 16: 16, 32, 48, 64, 80...
12: 12, 24, 36, 48, 60, 72, 84, 96, 108...
Answer: 48

3) 25: 25, 50, 75, 100, 125, 150, 175, 200...
30: 30, 60, 90, 120, 150, 180, 210...
Answer:150

4) 40: 40, 80, 120, 160, 200, 240, 280, 320, 360...
50: 50, 100, 150, 200, 250, 300, 350...
Answer: 200

5) 18:18, 36, 54, 72, 90, 108, 126
24: 24, 48, 72, 96, 120
Answer:72

Answer 2

`12|2\\.\ 6|2\\.\ 3|3\\.\ 1|\\12=2*2*\fbox3\\\\21|3\\.\ 7|7\\.\ 1|\\21=\fbox3*7\\\\LCM(12;\ 21)=\fbox3*2*2*7=84`



`16|2\\.\ 8|2\\.\ 4|2\\.\ 2|2\\.\ 1|\\16=\fbox2*\fbox2*2*2\\\\12|2\\.\ 6|2\\.\ 3|3\\.\ 1|\\12=\fbox2*\fbox2*3\\\\LCM(16;\ 12)=\fbox2*\fbox2*2*2*3=48`



`25|5\\.\ 5|5\\.\ 1|\\25=\fbox5*5\\\\30|2\\15|3\\.\ 5|5\\.\ 1|\\30=2*3*\fbox5\\\\LCM(25;\ 30)=\fbox5*5*2*3=150`



`40|2\\20|2\\10|2\\.\ 5|5\\.\ 1|\\40=\fbox2*2*2*\fbox5\\\\50|2\\25|5\\.\ 5|5\\.\ 1|\\50=\fbox2*\fbox5*5\\\\LCM(40;\ 50)=\fbox2*\fbox5*2*2*5=200`



`18|2\\.\ 9|3\\.\ 3|3\\.\ 1|\\18=\fbox2*\fbox3*3\\\\24|2\\12|2\\.\ 6|2\\.\ 3|3\\.\ 1|\\24=\fbox2*2*2*\fbox3\\\\LCM(18;\ 24)=\fbox2*\fbox3*3*2*2=72`