How 9 Cheenta students ranked in top 100 in ISI and CMI Entrances?

Learn MoreContent

[hide]

Try this TOMATO problem from I.S.I. B.Stat Entrance Objective Problem based on Integer and Divisibility.

Every integer of form \((n^{3}-n)(n-2)\) for n=3,4,..... is

- divisible by 12 but not always divisible by 24
- divisible by 6 but not always divisible by 12
- divisible by 24 but not always divisible by 48
- divisible by 9

Logic

Integers

Divisibility

But try the problem first...

Answer: divisible by 6 but not always divisible by 12

Source

Suggested Reading

B.Stat Objective Question 69

Challenges and Thrills of Pre-College Mathematics by University Press

First hint

\((n^{3}-n)(n-2)=n(n^{2}-1)(n-2)=(n-1)n(n+1)(n-2)\)

Second Hint

(n-1)n(n+1) is divisible by 3 and any two consecutive integers is divisible by 2 gcd(2,3)=1

Final Step

then 6|(n-1)n(n+1) and minimum (n-2)=1 for n=3,4,.... then \((n^{3}-n)(n-2)\) divisible by 6 but not always divisible by 12.

- https://www.cheenta.com/rational-number-and-integer-prmo-2019-question-9/
- https://www.youtube.com/watch?v=lBPFR9xequA

Cheenta is a knowledge partner of Aditya Birla Education Academy

Advanced Mathematical Science. Taught by olympians, researchers and true masters of the subject.

JOIN TRIAL