type 3 money multiples in ‘n’ years Section-Wise Topic Notes With Detailed Explanation And Example Questions

Answer: (c)

The sum gets doubled in 5 years and tripled in 12 years.

Clearly rate of interest for 12 years will be lower.

Let Principal be x.

then, Rate = ${SI × 100}/\text"Principal × Time"$

= ${2x × 100}/{x × 12} = 50/3 = 16{2}/3%$

Using Rule 3,

$R_1 = {(2 - 1)}/5 × 100%$ = 20%

$R_2 = {(3 - 1)}/12 × 100% = 16{2}/3%$

Lower rate of interest =16$2/3%$

Answer: (d)

Principal = Rs.x (let)

Amount = Rs.5x

Interest = Rs.(5x - x) = Rs.4x

Rate = ${S.I. × 100}/\text"Principal × Time"$

= ${4x × 100}/{x × 8}$ = 50% per annum

Answer: (a)

Case-I

Let the principal be x

Amount = 3x

Interest = 2x

Time = 20 years

I = $\text"PRT"/100$

2x = ${x × R × 20}/100$ ⇒ R = 10%

Case-II

I = x, P = x, R = 10, T = ?

I = $\text"PRT"/100$

x = ${x × 10 × T}/100$ ⇒ T = 10 years.

Using Rule 3,

R% = ${(3 - 1)}/20$ × 100% = 10%

Now, T = ${(n - 1)}/R$ years

T = ${2 - 1}/10 × 100$ = 10 years

Answer: (d)

Case I,

Interest = Principal

Rate = ${Interest × 100}/\text"Principal × Time"$

= $100/7%$ per annum

Case II,

Interest = 3 × Principal

Time = ${Interest × 100}/\text"Principal × Time"$

= ${3 × 100}/{100/7}$ = 3 × 7 = 21 years

Answer: (a)

Rate = R% per annum

Time = $R/2$ years

Rate = ${SI × 100}/\text"Principal × Time"$

R = $8/25 × 100/{R/2}$

$R^2 = {8 × 200}/25$ = 64

R = $√{64}$ = 8% per annum