In how many ways can different books be arranged in a row on a shelf if two particular books must be together?
Answer and explanation
Correct answer: C.
- Step 1: Treat the two books as one block: items can be arranged in ways.
- Step 2: The two books can swap inside the block, so the total is .
Answer
.
Why not the others: is what you get if you ignore the condition. is what you get if you forget that the two books can swap places. is what you get if you treat three items as stuck together.
Practise more Pure Maths: Coordinate Geometry, Vectors and Counting.
Free questions with an explanation for every one, and full timed GCE Advanced Level (Sri Lanka) mock tests.
More Pure Maths: Coordinate Geometry, Vectors and Counting questions
- The point lies outside the circle with centre and radius . Find the length of a tangent from to the circle.
- A bag contains 5 red and 7 blue balls. Two balls are drawn without replacement. Find the probability that both are red.
- Find the radius of the circle .
- Find the -intercept of the line through and .
- Find the radius of the circle .
- Find the -intercept of the line through and .