A sum of Rs.10 is lent by a child to his friend to be returned in 11 monthly instalments of Rs.1 each, the interest being simple. The rate of interest is:
Answer & explanation
Correct answer: option 2
Interest = 1 Rs
Interest = \(\frac{Principal ×Rate×Time}{100}\)
Total Interest for every month=
1 = \(\frac{10×R×1}{100×12}\)+\(\frac{9×R×1}{100×12}\)------\(\frac{1×R×1}{100×12}\)
1 = \(\frac{(10+9+8-----1)×R×1}{100×12}\)
(Sum = 10+9+8-----1=\(\frac{10×11}{2}\)=55)
1=\(\frac{55×R×1}{1200}\)
R=\(\frac{240}{11}\) OR 21 \(\frac{9}{11}\)%