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

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)

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: (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$2/3%$