# CBSE Class 10 Answered

**maths doubt**

Asked by dixitayush414 | 04 Jan, 2023, 09:03: PM

Expert Answer

Qn.(17)

total number of trees planted by students = 3 ( 1 +2 +3 + ......................+10+11+12 )

multiplication factor 3 in above expression is for 3 sections in each class .

total number of trees planted by students = 3 × (12 × 13) / 2 = 234

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Qn.(18)

Spiral consists of 13 semi-circle as shown in figure.

Radius of each semicircle increases by 0.5 cm from previous one and starting radius is 0.5 .

Total length = ( 0.5 + 1.0 + 1.5 + ......................6.0 + 6.5 ) cm

Total length = × 0.5 ( 1 + 2 + 3 + ......................12 + 13 ) cm

Total length = × 0.5 × [ (13 × 14 ) /2 ] = 45.5 cm

Answered by Thiyagarajan K | 04 Jan, 2023, 10:08: PM

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