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

Answer: (c)

Principal = Rs.P and time = T years

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

According to the question,

P + ${PT × 5}/100$ = 2200

P + ${PT}/20$ = 2200 ...(i)

Again, ${PT × 8}/100 - {PT × 5}/100$

= 2320 - 2200

${3PT}/100$ = 120

PT = ${120 × 100}/3$ = 4000 ...(ii)

From equation (i),

P + $4000/20$ = 2200

P = 2200 - 200 = Rs. 2000

From equation (ii),

PT = 4000

T = $4000/2000$ = 2 years

Alternative Method

Difference in rates

= 8 - 5 = 3%

Since,3% ≡ 2320 - 2200 = 120

5% ≡ $120/3$ × 5 = 200

Principal = Rs.(2200 - 200) = Rs.2000

Time = ${200 × 100}/{2000 × 5}$ = 2 years

Answer: (d)

According to the question,

Principal = Rs.x.

Interest = Rs.x.

Time = $50/3$ years

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

= ${x × 100}/{x × {50/3}}$

= ${100 × 3}/50$ = 6% per annum

Answer: (a)

Using Rule 1,

SI = Rs.(7200–6000) = Rs.1200

SI = $\text"PRT"/100$

1200 = ${6000 × R × 4}/100$

R = ${1200 × 100}/{6000 × 4}$ = 5%

New rate of R = 5×1.5 = 7.5%

Then, SI = ${6000 × 7.5 × 5}/100$ = Rs.2250

Amount = Rs.(6000 + 2250) = Rs.8250

Answer: (d)

Let the principal be x.

Case-I

$2x = {x × R × 15}/100$

R = ${2 × 100}/15 = 40/3%$

Case-II

SI = 4x

$4x = {x × 40 × T}/300$

T = ${4 × 300}/40 = 30$ years

Using Rule 3,

R = ${(3 - 1)}/15 × 100%$

= $2/15 × 100%$

= $2/3 × 20% = 40/3%$

T = ${(n - 1)}/R$ Years

= ${(5 - 1)}/{40/3} × 100$ = 30 years.

Answer: (c)

Let principal be Rs. x.

Amount = Rs.2x

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

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

= ${x × 100}/{x × 8} = 25/2$

= 12$1/2%$ per annum

Answer: (a)

Principal = Rs.x

Amount = Rs.2x

Interest = 2x - x = Rs.x

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

= ${x × 100}/{x × 8} = 25/2$ = 12.5 % per annum

Using Rule 3,

R % = ${(n - 1)}/T × 100%$

= ${(2 - 1)}/8 × 100%$ = 12.5%