 Hello and welcome to the session. The given question says, a radio is available for Rs. 1500 cash or for Rs. 360 cash down payment followed by three equal monthly installments of Rs. 390. Find the rate of interest charged under the installment screen. Let's start with the solution. First, we are given that cash price of radio denoting it by CP is equal to Rs. 1500. Second, cash down payment that is denoted by DP is equal to Rs. 360. Therefore, the balance amount which is due denoting it by BT is equal to CP minus DP which is equal to Rs. 1500 minus 360 and this is further equal to Rs. 1140. Also, we are given that value of each installment denoting it by small p is equal to Rs. 390 and he has paid three installments that is the number of installments is equal to three. And therefore, value of all installments is given by the number of installment and the value of installment that is P into N which is equal to Rs. 390 into 3 and this is equal to Rs. 1170. Now, let the rate of interest be equal to R% and therefore the interest charged is given by the value of all the installments minus the balance due and this is equal to Rs. 1170 minus 1140 which is the balance due. And this is further equal to Rs. 30. Now, the next step is principle for the first month is which is the balance due is equal to 1140 rupees. Similarly, principle for the second month is given by the difference of balance due and the first installment which is equal to Rs. 750 that is we get when we subtract the first installment from the principle of the first month that is 1140 minus 390. Then we shall find the principle for the third month and this is equal to Rs. 750 minus 390 and this is equal to Rs. 360. So, this we get on subtracting the installment from the second principle that is the principle for the second month. Total principle is equal to the sum of these three principles for the first month, second month and third month and this is equal to Rs. 2250. Now in the next step as we know that interest is equal to principle into R% into time therefore here interest as we have calculated above is Rs. 30 and the total principle again this we have calculated in the above steps is equal to Rs. 2250. And rate percent is R divided by 100 and time is given by 1 divided by 12 that is one month by substituting all these values in this formulae we have increased as 30 which is our sixth step is equal to principle that is 2250 into rate percent that is R divided by 100 into the time which is 1 divided by 12. Therefore on cost multiplying we have R is equal to 30 into 100 into 12 divided by 2250 which on simplifying comes equal to 16. Therefore our answer is rate of interest is 16% per annum. So, this completes the session. Bye and take care.