## 2019 PSLE Question on finding Diameter

- Details
- Parent Category: geometry
- Category: 1. 2D Shapes
- Created: Wednesday, 02 October 2019 13:54
- Last Updated: Wednesday, 02 October 2019 15:05
- Published: Wednesday, 02 October 2019 13:54
- Written by Loo Kang Wee
- Hits: 1865

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## 2019 PSLE Question on finding Diameter

### Method 1 by the Boring physics teacher https://youtu.be/JuGNaORvxvs

Shift circle C by 12 cm. Therefore, by symmetry looking at the circle B, the diameter is 10+16+10 where 10 is from the shifting of 22-12, the first 10 is by symmetry. The diameter is 36 cm.

### Method 2 by Julie Choy

Shift circle B, C, D and E to the extreme left to align them up. So, the circle C is the odd one out. Then the diameter is sum of the bottom numbers subtract the sum of the top numbers, leading to 22+16+22 - (12+12) =36 cm.

### Method 3

Shift circle D to the extreme left align with circle A. Shift circle E to the extreme right align with circle C. So, the bottom numbers add up is equal to the 2 top numbers plus diameter B. Therefore, the diameter is sum of the bottom numbers subtract the sum of the top numbers, leading to 22+16+22 - (12+12) =36 cm.

### Conclusion

Therefore, the principle to solving this kind of problem is to look out for a pattern that leads to top set of numbers - bottom set of numbers, is the odd length out which is the diameter in this case.

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