1. Yellow & Red Cards

There are 100 cards, and they are numbered from 1-100 on both sides. One face of a card is of red color & the other face is yellow. John spreads all the cards in sequence i.e from card numbered 1 to 100 with all cards facing red.
He flip all the card that are divisible by 2 and than again divisible by 3. How many red cards will he be left with?

2. Originally Posted by u2_wa
There are 100 cards, and they are numbered from 1-100 on both sides. One face of a card is of red color & the other face is yellow. John spreads all the cards in sequence i.e from card numbered 1 to 100 with all cards facing red.
He flip all the card that are divisible by 2 and than again divisible by 3. How many red cards will he be left with?
Let a be the number of cards between 1 and 100 inclusive that are divisible by 2.

Let b be the number of cards between 1 and 100 inclusive that are divisible by 3.

Let c be the number of cards between 1 and 100 inclusive that are divisible by 6.

Then the answer is 100 - (a + b - c).