## Ask Singapore Homework?

Upload a photo of a Singapore homework and someone will email you the solution for free.

## Question

Secondary 1 | Maths

** One Answer Below **

Anyone can contribute an answer, even non-tutors.

**Answer This Question**

Permutations and Combinations Question. Pls help thanks!!

Thanks!!

Counted from one side of the triangle at a time to avoid double counting. Tried from each of the 3 sides and got 90 for all

We choose the left side and base of the △ first. There are 6 possible lines to choose from.

Number of ways to choose 2 lines to make the left side and the base = 6C2 = 15

Now we need the right side to form the △. There are 4 lines that extend from the left vertex of the big △ to its right side, for us to use.

Number of ways to choose a right side

= 4 (or 4C1 which = 4 anyway)

Total number of triangles here

= 15 x 4

= 60

Case ② : base is a line from the left vertex of the big △ to its right side.

We choose the right side and base of the△ first. There are 5 possible lines to choose from. We cannot consider the bottom horizontal line as it has been used in case ①. It would result in double counting if we did.

Number of ways to choose 2 lines to make the right side and the base = 5C2 = 10

Now we need the left side to form the △. There are 3 lines that extend from the right vertex of the big △ to its left side, for us to use.

Number of ways to choose a right side

= 3 (or 3C1 which = 3 anyway)

Total number of triangles here

= 10 x 3

= 30

Total triangles = 60 + 30 = 90

Not easy at all. It would be hard for A level students, and to think they give it you all at Sec 1..

### See 1 Answer

*done*{{ upvoteCount }} Upvotes

*clear*{{ downvoteCount * -1 }} Downvotes

I hope this will help you