A man buys a watch for Rs. 1950 in cash and sells it for Rs. 2200 at a credit of 1 year. If the rate of interest is 10% per annum, the man:

A. 1
B. 14
C. 20
D. 21
Clearly, the numbers which have 1 or 9 in the unit’s digit, have squares that end in the digit 1. Such numbers from 1 to 70 are 1, 9, 11, 19, 21, 29, 31, 39, 41, 49, 51, 59, 61, 69.
Number of such numbers = 14.
Required percentage = (14/70 * 100) = 20%

A. Rs. 6000
B. Rs. 18000
C. Rs. 20000
D. Rs. 14000
Explanation:
5 % A = 15 % B and 10 % B = 20 % C.
A/20 = 3B/20 and B/10 = C/5
or B = 2C. A/20 = 3/20 × 2c = 3/10
C = 3/10 × 2000 = 600
A = (600 × 20) = 12000,
B = (2 × 2000) = 4000
A + B + C = (12000 + 4000 + 2000) = 18000
Therefore, Rs. 18000/-