Page 47 - NUMINO Challenge_B1

Type 5-1 Crossing Out Numbers from a Calendar

Two players want to play a calendar July
game. They take turns crossing out
numbers that are less than, or equal to, Sun Mon Tue Wed Thu Fri Sat
the number indicating the month. For
example, if it is April, a player can cross 12 3
out up to 4 days on his turn. The player 4 5 6 7 8 9 10
who crosses out the last date loses. For 11 12 13 14 15 16 17
the month of July, how many days should 18 19 20 21 22 23 24
a player cross out on the first turn, in 25 26 27 28 29 30 31
order to always win?

1 Which date must you cross out on your last turn, so that you will always
win?

2 Which date should be crossed out before the date in 1 ?

3 Thinking backwards, write down all the dates that should be crossed out in
order to cross out the 30th.

4 Find the earliest date among the dates in 3 , and explain the winning
strategy for the game.

5 You and a friend are playing this game with a November calendar. Explain
the winning strategy for this game. Note that November has 30 days.

44 NUMINO Challenge B1