LCM for 20 and 40

The first method to find LCM for numbers 20 and 40 is to find Greatest Common Factor (GCF) of these numbers. Here's the formula:

LCM = (Number1 × Number2) ÷ GCF

GCF of numbers 20 and 40 is 20, so

LCM = (20 × 40) ÷ 20

LCM = 800 ÷ 20

LCM = 40

The second method to find LCM for numbers 20 and 40 is to list out the common multiples for both nubmers and pick the first which matching:

Multiples of 20: 20, 40, 60, 80

Multiples of 40: 40, 80, 120, 160, 200, 240, 280, 320, 360, 400, 440, 480, 520, 560, 600, 640, 680, 720, 760, 800, 840, 880, 920, 960, 1000, 1040, 1080, 1120, 1160, 1200, 1240, 1280, 1320, 1360, 1400, 1440, 1480, 1520, 1560, 1600, 1640, 1680, 1720, 1760, 1800, 1840, 1880, 1920, 1960, 2000, 2040, 2080, 2120, 2160, 2200, 2240, 2280, 2320, 2360, 2400, 2440, 2480, 2520, 2560, 2600, 2640, 2680, 2720, 2760, 2800, 2840, 2880, 2920, 2960, 3000, 3040, 3080, 3120, 3160, 3200, 3240, 3280, 3320, 3360, 3400, 3440, 3480, 3520, 3560, 3600, 3640, 3680, 3720, 3760, 3800, 3840, 3880, 3920, 3960, 4000, 4040, 4080, 4120, 4160, 4200, 4240, 4280, 4320, 4360, 4400, 4440, 4480, 4520, 4560, 4600, 4640, 4680, 4720, 4760, 4800, 4840, 4880, 4920, 4960, 5000, 5040, 5080, 5120, 5160, 5200, 5240, 5280, 5320, 5360, 5400, 5440, 5480, 5520, 5560, 5600, 5640, 5680, 5720, 5760, 5800, 5840, 5880, 5920, 5960, 6000, 6040, 6080, 6120, 6160, 6200, 6240, 6280, 6320, 6360, 6400, 6440, 6480, 6520, 6560, 6600, 6640, 6680, 6720, 6760, 6800, 6840, 6880, 6920, 6960, 7000, 7040, 7080, 7120, 7160, 7200, 7240, 7280, 7320, 7360, 7400, 7440, 7480, 7520, 7560, 7600, 7640, 7680, 7720, 7760, 7800, 7840, 7880, 7920, 7960, 8000, 8040, 8080, 8120, 8160, 8200, 8240, 8280, 8320, 8360, 8400, 8440, 8480, 8520, 8560, 8600, 8640, 8680, 8720, 8760, 8800, 8840, 8880, 8920, 8960, 9000, 9040, 9080, 9120, 9160, 9200, 9240, 9280, 9320, 9360, 9400, 9440, 9480, 9520, 9560, 9600, 9640, 9680, 9720, 9760, 9800, 9840, 9880, 9920, 9960, 10000, 10040, 10080, 10120, 10160, 10200, 10240, 10280, 10320, 10360, 10400, 10440, 10480, 10520, 10560, 10600, 10640, 10680, 10720, 10760, 10800, 10840, 10880, 10920, 10960, 11000, 11040, 11080, 11120, 11160, 11200, 11240, 11280, 11320, 11360, 11400, 11440, 11480, 11520, 11560, 11600, 11640, 11680, 11720, 11760, 11800, 11840, 11880, 11920, 11960, 12000, 12040, 12080, 12120, 12160, 12200, 12240, 12280, 12320, 12360, 12400, 12440, 12480, 12520, 12560, 12600, 12640, 12680, 12720, 12760, 12800, 12840, 12880, 12920, 12960, 13000, 13040, 13080, 13120, 13160, 13200, 13240, 13280, 13320, 13360, 13400, 13440, 13480, 13520, 13560, 13600, 13640, 13680, 13720, 13760, 13800, 13840, 13880, 13920, 13960, 14000, 14040, 14080, 14120, 14160, 14200, 14240, 14280, 14320, 14360, 14400, 14440, 14480, 14520, 14560, 14600, 14640, 14680, 14720, 14760, 14800, 14840, 14880, 14920, 14960, 15000, 15040, 15080, 15120, 15160, 15200, 15240, 15280, 15320, 15360, 15400, 15440, 15480, 15520, 15560, 15600, 15640, 15680, 15720, 15760, 15800, 15840, 15880, 15920, 15960, 16000, 16040, 16080, 16120, 16160, 16200, 16240, 16280, 16320, 16360, 16400, 16440, 16480, 16520, 16560, 16600, 16640, 16680, 16720, 16760, 16800, 16840, 16880, 16920, 16960, 17000, 17040, 17080, 17120, 17160, 17200, 17240, 17280, 17320, 17360, 17400, 17440, 17480, 17520, 17560, 17600, 17640, 17680, 17720, 17760, 17800, 17840, 17880, 17920, 17960, 18000, 18040, 18080, 18120, 18160, 18200, 18240, 18280, 18320, 18360, 18400, 18440, 18480, 18520, 18560, 18600, 18640, 18680, 18720, 18760, 18800, 18840, 18880, 18920, 18960, 19000, 19040, 19080, 19120, 19160, 19200, 19240, 19280, 19320, 19360, 19400, 19440, 19480, 19520, 19560, 19600, 19640, 19680, 19720, 19760, 19800, 19840, 19880, 19920, 19960, 20000, 20040, 20080, 20120, 20160, 20200, 20240, 20280, 20320, 20360, 20400, 20440, 20480, 20520, 20560, 20600, 20640, 20680, 20720, 20760, 20800, 20840, 20880, 20920, 20960, 21000, 21040, 21080, 21120, 21160, 21200, 21240, 21280, 21320, 21360, 21400, 21440, 21480, 21520, 21560, 21600, 21640, 21680, 21720, 21760, 21800, 21840, 21880, 21920, 21960, 22000, 22040, 22080, 22120, 22160, 22200, 22240, 22280, 22320, 22360, 22400, 22440, 22480, 22520, 22560, 22600, 22640, 22680, 22720, 22760, 22800, 22840, 22880, 22920, 22960, 23000, 23040, 23080, 23120, 23160, 23200, 23240, 23280, 23320, 23360, 23400, 23440, 23480, 23520, 23560, 23600, 23640, 23680, 23720, 23760, 23800, 23840, 23880, 23920, 23960, 24000, 24040, 24080, 24120, 24160, 24200, 24240, 24280, 24320, 24360, 24400, 24440, 24480, 24520, 24560, 24600, 24640, 24680, 24720, 24760, 24800, 24840, 24880, 24920, 24960, 25000, 25040, 25080, 25120, 25160, 25200, 25240, 25280, 25320, 25360, 25400, 25440, 25480, 25520, 25560, 25600, 25640, 25680, 25720, 25760, 25800, 25840, 25880, 25920, 25960, 26000, 26040, 26080, 26120, 26160, 26200, 26240, 26280, 26320, 26360, 26400, 26440, 26480, 26520, 26560, 26600, 26640, 26680, 26720, 26760, 26800, 26840, 26880, 26920, 26960, 27000, 27040, 27080, 27120, 27160, 27200, 27240, 27280, 27320, 27360, 27400, 27440, 27480, 27520, 27560, 27600, 27640, 27680, 27720, 27760, 27800, 27840, 27880, 27920, 27960, 28000, 28040, 28080, 28120, 28160, 28200, 28240, 28280, 28320, 28360, 28400, 28440, 28480, 28520, 28560, 28600, 28640, 28680, 28720, 28760, 28800, 28840, 28880, 28920, 28960, 29000, 29040, 29080, 29120, 29160, 29200, 29240, 29280, 29320, 29360, 29400, 29440, 29480, 29520, 29560, 29600, 29640, 29680, 29720, 29760, 29800, 29840, 29880, 29920, 29960, 30000, 30040, 30080, 30120, 30160, 30200, 30240, 30280, 30320, 30360, 30400, 30440, 30480, 30520, 30560, 30600, 30640, 30680, 30720, 30760, 30800, 30840, 30880, 30920, 30960, 31000, 31040, 31080, 31120, 31160, 31200, 31240, 31280, 31320, 31360, 31400, 31440, 31480, 31520, 31560, 31600, 31640, 31680, 31720, 31760, 31800, 31840, 31880, 31920, 31960, 32000, 32040, 32080, 32120, 32160, 32200, 32240, 32280, 32320, 32360, 32400, 32440, 32480, 32520, 32560, 32600, 32640, 32680, 32720, 32760, 32800, 32840, 32880, 32920, 32960, 33000, 33040, 33080, 33120, 33160, 33200, 33240, 33280, 33320, 33360, 33400, 33440, 33480, 33520, 33560, 33600, 33640, 33680, 33720, 33760, 33800, 33840, 33880, 33920, 33960, 34000, 34040, 34080, 34120, 34160, 34200, 34240, 34280, 34320, 34360, 34400, 34440, 34480, 34520, 34560, 34600, 34640, 34680, 34720, 34760, 34800, 34840, 34880, 34920, 34960, 35000, 35040, 35080, 35120, 35160, 35200, 35240, 35280, 35320, 35360, 35400, 35440, 35480, 35520, 35560, 35600, 35640, 35680, 35720, 35760, 35800, 35840, 35880, 35920, 35960, 36000, 36040, 36080, 36120, 36160, 36200, 36240, 36280, 36320, 36360, 36400, 36440, 36480, 36520, 36560, 36600, 36640, 36680, 36720, 36760, 36800, 36840, 36880, 36920, 36960, 37000, 37040, 37080, 37120, 37160, 37200, 37240, 37280, 37320, 37360, 37400, 37440, 37480, 37520, 37560, 37600, 37640, 37680, 37720, 37760, 37800, 37840, 37880, 37920, 37960, 38000, 38040, 38080, 38120, 38160, 38200, 38240, 38280, 38320, 38360, 38400, 38440, 38480, 38520, 38560, 38600, 38640, 38680, 38720, 38760, 38800, 38840, 38880, 38920, 38960, 39000, 39040, 39080, 39120, 39160, 39200, 39240, 39280, 39320, 39360, 39400, 39440, 39480, 39520, 39560, 39600, 39640, 39680, 39720, 39760, 39800, 39840, 39880, 39920, 39960, 40000, [...], 40

So the LCM for 20 and 40 is 40

Another method to find LCM for numbers 20 and 40 is to list all Prime Factors for both numbers and multiply the highest exponent prime factors: