In a school, students thought of planting trees in and around the school to reduce air pollution. It was decided that the number of trees, that each section of each class will plant, will be the same as the class, in which they are studying, e.g., a section of Class $\mathrm{I}$ will plant $1$ tree, a section of Class $\mathrm{II}$ will plant $2$ trees and so on till Class $\mathrm{XII}$. There are three sections of each class. How many trees will be planted by the students?

A spiral is made up of successive semicircles, with centres alternately at $A$ and $B$, starting with centre at $A$, of radii $0.5 \mathrm{cm}, 1.0 \mathrm{cm}, 1.5 \mathrm{cm}, 2.0 \mathrm{cm}$, ... as shown in Figure. What is the total length of such a spiral made up of thirteen consecutive semicircles? (Take $\mathrm{\pi }=\frac{22}{7}$)

$200$ logs are stacked in the following manner: $20$ logs in the bottom row, $19$ in the next row, $18$ in the row next to it and so on. In how many rows are the $200$ logs placed and how many logs are in the top row?

In a bucket and ball race, a bucket is placed at the starting point, which is $5 \mathrm{m}$ from the first ball, and the other balls are placed $3 \mathrm{m}$ apart in a straight line. There are ten balls in the line.

A competitor starts from the bucket, picks up the nearest ball, runs back with it, drops it in the bucket, runs back to pick up the next ball, runs to the bucket to drop it in, and she continues in the same way until all the balls are in the bucket. What is the total distance the competitor has to run? [No need to mention units in the answer box]

[Hint: To pick up the first ball and the second ball, the total distance (in metres) run by a competitor is $2\times 5+2\times \left(5+3\right)$]

In which of the following situations, does the list of numbers involved is in the form of a GP?

Salary of Sharmila, when her salary is $₹ 5,00,000$ for the first year and expected to receive yearly increase of $10\%$.