Problema Solution
There are 13 steps in Demi's staircase. One step squeaks every time someone steps on it. Last week one friend started on step 1 and climbed to the top taking 2 steps at a time. A second friend started from the floor and climbed to step 13 by taking 3 steps up and 1 down. Even though Demi was listening carefully, she heard no squeak either time. Which step is squeaky?
Answer provided by our tutors
we will find the steps that don't squeak
one friend started on step 1 and climbed to the top taking 2 steps at a time:
1, 3, 5, 7, 9, 11, 13
second friend started from the floor and climbed to step 13 by taking 3 steps up and 1 down
3, 2, 5, 4, 7, 6, 9, 8, 11, 10, 13
the only number that is not mentioned in the sequences is 12 thus the 12th step is squeaky.