model 1 basic compound interest using formula Section-Wise Topic Notes With Detailed Explanation And Example Questions

MOST IMPORTANT quantitative aptitude - 6 EXERCISES

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The following question based on compound interest topic of quantitative aptitude

Questions : The sum of money that yields a compound interest of Rs.420 during the second year at 5% p.a is

(a) Rs.21,000

(b) Rs.4,000

(c) Rs.8,000

(d) Rs.42,000

The correct answers to the above question in:

Answer: (c)

Using Rule 1,

CI = P$[(1 + R/100)^T –1] - {PR}/100$

420 = P$[(1 + 5/100)^2 - 1] - {P × 5}/100$

420 = P$[(21/20)^2 - 1] - {5P}/100$

420 = ${41P}/400 - {5P}/100 = {21P}/400$

P = ${420 × 400}/21$ = Rs.8000

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Read more basic problems using formula Based Quantitative Aptitude Questions and Answers

Question : 1

An amount of Rs.6,000 lent at 5% per annum compound interest for 2 years will become

a) Rs.6,615

b) Rs.600

c) Rs.6,610

d) Rs.6,600

Answer: (a)

Using Rule 1,

A = P$(1 + R/100)^T$

= 6000$(1 + 5/100)^2$

= 6000 × $21/20 × 21/20$ = Rs.6615

Question : 2

The compound interest on Rs.2000 in 2 years if the rate of interest is 4% per annum for the first year and 3% per annum for the second year, will be

a) Rs.143.40

b) Rs.142.40

c) Rs.141.40

d) Rs.140.40

Answer: (b)

Using Rule 3,

Amount = $2000(1 + 4/100)(1 + 3/100)$

= 2000 ×1.04 ×1.03 = Rs.2142.40

CI = Rs.(2142.40 - 2000) = Rs.142.40

Question : 3

The compound interest on Rs.10,000 in 2 years at 4% per annum, the interest being compounded half-yearly, is :

a) Rs.828. 82

b) Rs.636.80

c) Rs.912. 86

d) Rs.824.32

Answer: (d)

Using Rule 1,

A = 10,000$(1 + 2/100)^4$

=10,000$(51/50)^4$ =10824.3216

Interest = 10,824.3216 - 10,000

= Rs.824.32

Question : 4

A principal of Rs.10,000, after 2 years compounded annually, the rate of interest being 10% per annum during the first year and 12% per annum during the second year (in rupees) will amount to :

a) Rs.11,320

b) Rs.12,000

c) Rs.12,500

d) Rs.12,320

Answer: (d)

Using Rule 3,

A = P$(1 + r_1/100)(1 + r_2/100)$

= 10000$(1 + 10/100)(1 + 12/100)$

= 10000 × $11/10 × 28/25$ = Rs.12320

Question : 5

In what time Rs.8,000 will amount to Rs.9,261 at 10% per annum compound interest, when the interest is compounded half yearly ?

a) 2 years

b) 3$1/2$ years

c) 2$1/2$ years

d) 1$1/2$ years

Answer: (d)

Using Rule 1 and 2,

Interest is compounded half yearly.

Rate of interest = 5%

Time = $n/2$ years (let)

or n half-years

A = P$(1 + R/100)^T$

9261 = 8000$(1 + 5/100)^n$

$9261/8000 = (21/20)^n$

$(21/20)^3 = (21/20)^n$

n = 3 half years

= $3/2$ years = $1{1}/2$ years

Question : 6

A sum of Rs.8000 will amount to Rs.8820 in 2 years if the interest is calculated every year. The rate of compound interest is

a) 5%

b) 6%

c) 3%

d) 7%

Answer: (a)

Using Rule 1,

If the rate of C.I. be r% per annum, then

A = P$(1 + R/100)^T$

8820 = 8000$(1 + r/100)^2$

$8820/8000 = (1 + r/100)^2$

$441/400 = (21/20)^2 = (1 + r/100)^2$

$1 + r/100 = 21/20$

$r/100 = 21/20 - 1 = 1/20$

r = $1/20$ × 100

r = 5% per annum

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