Write the first and the last numbers of the `10^(th)` line.

Observe the number pattern made using terms of an arithmetic sequence 2, 6,10, ... . Find the first and the last numbers in the 20th line.

Which is the last number in the 30^(th) row?

Write the sum of first n natural numbers.

. Which is the first number in the 30^(th) row?

Find the sum of all the numbers in the first ten lines.

Calculate the wavelength of the first and the last line in the Balmer series of the hydrogen spectrum.

Consider the multiples of 7 in between 100 and 500. What are the first and last numbers ?

The fourth, seventh and the last term of a G.P. are 10,80 and 2560 respectively. Find the first term and the number of terms in the G.P?