Tag: calculating and mental strategies 3

The sum of the $n$ natural numbers =$\frac{n\times (n+1)}{2}$
Here,$n=100$
$\therefore$ Sum=$\frac{100\times (100+1)}{2}$
$=\frac{100\times 101}{2}$
$=5050$
Option is D

The numbers can be easily counted.
5,15,25,35,45,50,51,52,53,54,55,56,57,58.59.65.75.85.95
Thus, there are 19 numbers

$\frac{7}{100} = 0.07$

$\frac{22}{1000} = 0.022$

correct option is C..

$122.5/1000$

cost of $20$ fans = Rs. $248.50$

The first decimal digit from the decimal point is the tenth, the second decimal digit from the decimal point is the hundredth and the third decimal digit from the decimal point is the thousandths digit. 

$150.75\div 0.6$

$143.6\div 2000=71.8\div 1000$
$=0.0718$