Simplify the following:  

$18-\left[18-\left\{18-\left(18-18\right)-18\right\}\right]$

Simplify the following:  

$150-\left[70-\left\{60-\left(30+20\right)-10\right\}\right]$

Members of an NGO decided to provide blankets to an old age home. For this purpose a sum of $Rs. 8435$ was collected and $35$ blankets were purchased. The old people were very happy with the blankets. They blessed the NGO members for their concern for the old people. What is the cost of one blanket donated? Name any two items that you can donate to an old age home.

Trees not only make the air pure but also beautify the environment. In a school, the members of Eco club were taken for a trip to a nearby nursery. As a part of a project the children planted $95$ saplings of different trees in the nursery. The cost of each sapling was $Rs. 175$. The children were very thrilled and happy with the project. What is the amount spent on the saplings? (Use distributive property) Name any two saplings that you will like to plant in your garden or nearby park.

Which of the following is meaningless 

The greatest two digit number exactly divisible by $17$ is

The smallest $5$-digit number formed by using the digits $3,0,1$ (Repetition of digits allowed) is 

Estimate:

$36+71-55$

Which of the following is not a natural number?