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

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: (a)

Case I,

Principal = Rs.x

Interest = Rs.x

Time = 6 years

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

= ${x × 100}/{x × 16} = 50/3%$ per annum

Case II,

Interest = ${x × 12 × 50}/{100 × 3}$ = Rs.2x

i.e., Amount is thrice the principal.

Answer: (c)

If the principal be x, the amount = 2x

SI = x

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

= ${x × 100}/{x × 15} = 20/3 = 6{2}/3$ years

Using Rule 3,

T = ${(n - 1)}/R × 100%$

= $({2 - 1}/15) × 100$

= $100/15 = 20/3$ Years

= 6$2/3$ years

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: (a)

Let principal be Rs.x.

Amount = Rs.2x

Interest = Rs.(2x - x) = Rs.x

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

= ${x × 100}/{x × 15} = 20/3$

= 6$2/3%$ per annum

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