Crosses and Squares
Two crosses can be put in three squares in three different ways, as follows.
In how many different ways can you put three crosses in five squares?
The Time Traveler's Schedule
If a time traveler moves forward in time by 15 years, and then goes back 10 years, and finally moves forward 5 years, she finds herself in the year 2030. In what year did she originally start her time travel?
If we think of it we would need to do 5 choose 3 as there are 5 squares and you need to choose three crosses. 5 choose three is simply (5 ⨉ 4 ⨉ 3) / (1 ⨉ 2 ⨉ 3) which is 10.
ReplyDelete