Greatest common divisor and least common multiple
Find the largest number that divides two numbers (GCD) and the smallest number both divide (LCM).
For 12 and 18, the common divisors are 1, 2, 3 and 6, so the GCD is 6. The multiples 36, 72 and so on are shared, so the LCM is 36. The GCD helps simplify fractions; the LCM helps add them.
Classic Graphing 84
Start on the main screen: Press 2nd then mode (QUIT) to get back to the home screen. Pressing clear on a menu also backs out of it.
Open MATH, move right to NUM, and choose 9, gcd(. Type 12, a comma, 18 and close the bracket.
math▶912,18)enterFor the LCM, choose item 8 instead.
math▶812,18)enter
You should seegcd(12,18) 6 lcm(12,18) 36
Natural Scientific 991
Start on the main screen: Press MENU, then 1 (Calculate) to return to the main calculation screen. AC clears the line you are on.
Press OPTN and choose 8, GCD(. Type 12, press SHIFT with the close-bracket key for the comma, then 18.
OPTN812SHIFT,)18)=For the LCM, press OPTN and choose 9.
OPTN912SHIFT,)18)=
You should seeLCM(12,18) 36
Classic CAS
Start on the main screen: Press home to open the Home menu (Calculator, Graphs, Settings, and more). Choose Calculator, or press esc to go back to the calculation page.
Press menu, choose 2 (Number), then 5 for gcd(. Type 12, a comma and 18.
menu2512,18)enterFor the LCM, choose 6 from the same menu.
menu2612,18)enter
You should seegcd(12,18) lcm(12,18) 36
Tips
- Check yourself: GCD × LCM always equals the product of the two numbers. Here 6 × 36 = 12 × 18 = 216.