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⁞ Simple Interest

Aptitude ➤ Simple Interest ➤ 1

1. Principal:The money borrowed or lent out for a certain period is called the principal or the sum.

2. Interest: Extra money paid for using other's money is called interest.

3. Simple Interest (S.I.) : If the interest on a sum borrowed for a certain period is reckoned uniformly, then it is called simple interest.

Let Principal = P, Rate = R % per annum (p.a.) and Time = T years. Then,

(i) S.I. = (P × R × T ) / 100

(ii) P = (100×S.I)/(R×T) ;
R = (100×S.I)/(P×T)
T = (100×S.I)/(P×R)

Question 1
Q1.  Find the simple interest on Rs. 72,000 at 16 2/3 % per annum for 9 months.
 

Answer :  Rs. 9000


P = Rs.72000,
R = 50/3 % p.a
and T = 9/12 years = 3/4 years.

∴ S.I. = (P×R×T)/100 = Rs.(72,000×(50/3)×(3/4)×(1/100))= Rs.9000
⚔ DISCUSS

Question 2
Q2.  A sum of Rs. 468.75 was lent out at simple interest and at the end of 1 year 8 months the total amount was Rs. 500. Find the rate of interest per cent per annum.
 

Answer :  4 %


Here,
P = Rs. 468.75,     T=1 2/3  or 5/3 Years

I = Rs. (500 − 468.75) = Rs. 31.25
∴ Rate p.c. = [100 × 31.25]/ [468.75 × 3/5 ]
⇒ R = 100 × (3125/46875) × 3/5 = 4 %
⚔ DISCUSS

Question 3
Q3.  A sum at simple interests at 13 ½ % per annum amounts to Rs.2502.50 after 4 years find the sum.
 

Answer :  Rs. 1625


Let sum be Rs. x then ,
S.I.=Rs.(x × (27/2) × 4 × (1/100) ) = Rs.27x/50

∴ amount = (Rs. x + (27x/50)) = Rs.77x/50
∴ 77x/50 = 2502.50 ⇔ x = (2502.50 × 50)/77 = 1625

Hence , sum = Rs.1625.
⚔ DISCUSS

Question 4
Q4.  Mr. Thomas invested an amount of Rs. 13,900 divided in two different schemes A and B at the simple interest rate of 14 % p.a. and 11 % p.a. respectively. If the total amount of simple interest earned in 2 years be Rs. 3508, what was the amount invested in Scheme B ?
 

Answer :  Rs. 6400


Let the sum invested in Scheme A be Rs. x and that in Scheme B be Rs. (13900 - x).
Then,
[ (x × 14 × 2)/100 ] + [(13900 - x) × 11 × 2]/100 = 3508
⇒ 28x - 22x = 350800 - (13900 × 22)
⇒ 6x = 45000
⇒ x = 7500.

∴ sum invested in Scheme B = Rs. (13900 - 7500) = Rs. 6400.
⚔ DISCUSS

Question 5
Q5.  A sum of Rs. 800 amounts to Rs. 920 in 3 years at simple interest. If interest rate is increased by 3 %, it would amount to how much ?
 

Answer :  Rs. 992


S.I. = Rs. (920 - 800) = Rs. 120;
P = Rs. 800,
T = 3 yrs.

∴ R = ((100 × 120)/(800 × 3) ) % = 5 %.

∴ New Rate = ( 5 + 3 ) % = 8 %.
∴ New S.l. = Rs. (800 × 8 × 3)/100 = Rs. 192.

Hence, New amount = Rs.(800 + 192) = Rs. 992.
⚔ DISCUSS

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