The blog postings are about the Singapore Math. The readers can learn from the postings on Solving Singapore Primary School Mathematics. The blog presents the Math Concept, the Math Questions with solutions that teaches in Singapore Primary Schools. You or the kids can learn the skills to deal with the Math Modeling, the Math Problem Solving and the Problem Sum from Lower Primary School to Upper Primary School level after reading the blog postings. This posting is an upper primary school math question on Angles and Shapes.

Read the posting on **Sarin learns Lines and Angles (Math concept)** to understand the concept of lines and angles.

Read the posting on **Sarin learns Shapes and Solids in school (Math Concept)** to know about shapes.

*Challenge yourself with the question before look for the given solution‼!*

**Upper primary school mathematics question UPQ451**

The diagram shows a regular octagon ABCDEFGH. Given that GD//FE and angle BDG = *x*^{0}, find the value of *x*.

*Solution:*

An Octagon has 8 inner angles.

For a regular octagon,

All inner angles are equal.

The sum of the inner angles = 6 × 180^{0} = 1080^{0}

∠ DEF ∠ CDE = 1080^{0} ÷ 8 = 135^{0}

Given GD//EF

^{ }∠ GDE = 180^{0} – 135^{0} = 45^{0}

CB = CD and BCD form an isosceles triangle

∠ CDB = ∠ CBD

∠ CDB + ∠ CDB = 180^{0} – 135^{0} = 45^{0}

∠ CDB = 45^{0} ÷ 2 = 22.5^{0}

Therefore,

∠ BDG = *x*^{0} = 135^{0} – 22.5^{0} – 45^{0} = 67.5^{0}