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All numbers from 1 to 100 are written on the board. Kishor erases all numbers but those that are multiples of 3. Then Basu erases all numbers but those that are multiples of four and finally, of the remaining numbers. Komal erases all numbers that are not multiples of five. How many numbers are left on the board?

A.	60	B.	6
C.	8	D.	None of these

Answer and Explanation

Answer:60

Explanation:
Kishor erases all numbers and leaves only numbers divisibly by 3. So on the board we have 3, 6, 9, 12, … 99. A total of 33 numbers are left out. Basu erases all but multiples of 4. From 33 numbers only multiples of 12 will remain, i.e, 12, 24, 36,… 96. A total of 8 members are left out. Komal erases all numbers that are not multiples of 5. The numbers that are multiples of 5 will be left out. Only 60 is a multiple of 5. The numbers erased are 12, 24, 36, 48, 72, 84 and 96. A total of 7 numbers will be erased and one number, i.e 60, remains on the board.
Alternately, the numbers that are left on the board = Multiples of LCM of (3, 4, 5).
This equals to 60. Hence only one number remains on the board .

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