Question

Find least no of five digit exactly divisible by 15 16 18 20

Answer 1

Step 1 : Find the LCM of 15, 16, 18 and 20

15 = 3 × 5

16 = 2 × 2 × 2 × 2

18 = 2 × 3 × 3

20 = 2 × 2 × 5

LCM = 720

Step 2 : Divide the LCM by the smallest five digit number

LCM = 720

5-digit smallest number = 10000

$\dfrac{10000}{720}$ = 13.8 or 14 (approx.)

Step 3 : Multiply the LCM by the obtained number

720 × 14

➾ 10080

∴ The smallest five digit number exactly divisible by 15, 16, 18 and 20 is 10080

Answer 2

take LCM of 15,16,18,20

= 720

take Lowest five digit number which is 10000
divide it by 720

remainder 80

add it to 10000 +80= 10080


so the least 5 digit number is 10080 which is divisible by 15 ,16 ,18,20.

$10080$


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