A hundred deck is a deck consisting of 100 cards numbered from 1 to 100. Each card has the same number printed on both sides. One side of the card is red and
the other side of the card is yellow.
Sarai places all of the cards on a table with each card’s red side facing up. She
first flips over every card that has a number on it which is a multiple of 2. She
then flips over every card that has a number on it which is a multiple of 3.
After Sarai has finished, how many cards have their red side facing up?