63. What principal will gain $ 30 in 5 yr. at 6% ? SOLUTION. — $1 will gain $.30 in 5 yr. at 6%; it will take as ch principal to gain $30 as $.30 is contained times in $30, ich is 100 times. Therefore it will take a principal of $100 to n $30 in 5 yr. at 6%. Find the principal that will gain : - $36 in 3 yr. at 6% 67. $100 in 10 yr. at 6% 68. $24 in 4 yr. at 6% $56 in 2 yr. at 4% $20 in 5 yr. at 5% 70. $30 in 1 yr. 8 mo. at 9% 71. $21 in 1 yr. 2 mo. at 6% 72. $13 in 6 mo. 15 da. at 12% 73. $14.20 in 2 yr. 4 mo. 12 da. at 6% 74. $76.80 in 4 yr. 3 mo. 6 da. at 9% 75. $17.04 in 3 yr. 6 mo. 18 da. at 8% 76. What principal will amount to $720 in 3 yr. 6%? 4 mo. SOLUTION. -The interest of $1 for 3 yr. 4 mo. at 6% is $.20, - the amount is $1.20; it will take as many times $1 to ount to $720 as $1.20 is contained times in $720, which is 600 Therefore it will take $600 principal. es. Find the principal that will amount to: 78. $280 in 1 yr. 6 mo. at 8% 84. $412 in 6 mo. at 6% 85. In what time will $60 gain $ 15 at 5% ? SOLUTION. $60 will gain $3 in 1 year at 5%; it will take as many years to gain $15 as $3 is contained times in $15, which is 5 times. Therefore it will take 5 years. In what time will 86. $120 gain $14.40 at 6% ? 93. $300 gain $42 at 7% ? 94. In what time will $30 amount to $40 at 10% ? SOLUTION. - When $30 amounts to $40 the gain is $10. Since $30 will gain $3 in 1 yr. at 10%, it will take as long to gain $ 10 as $3 is contained times in $10, which is 33 times. Therefore it will take 3 yr., or 3 yr. 4 mo. In what time will 95. $60 amount to $75 at 5% ? 101. In what time will $5 double itself at 4% ? SOLUTION. This means "in what time will $5 gain $5 at 4%." In 1 yr., at 4%, $5 gains $.20; it will take as many years to gain $5 as $.20 is contained times in $5, which is 25 times, Therefore it will take 25 years to double itself. 102. In what time will any principal double itself at 5%? SOLUTION. Since in 1 yr. at 6% a principal gains 6% and since o double itself it must gain 100%, it will take as many years as 5% is contained times in 100%, or 16 years. 103. In what time will a given principal treble itself it 6% ? SUGGESTION. To treble itself a principal must gain 200%, to quadruple itself 300%, etc. Find the time in which a sum will double itself Find the time in which a sum will treble itself Find the time in which a sum will quadruple itself 122. At 6% 123. At 5% 124. At 4% 125. At 7% 126. In what time will $ 500 double itself at 6% ? 127. In what time will $175 double itself at 20% ? 128. In what time will $ 65 double itself at 3% ? 129. At what per cent will $ 500 gain $ 75 in 5 years? SOLUTION. At 1% $500 in 5 yr. gains $25; it will take as any % to gain $75 as $25 is contained times in $75, or 3%. At what per cent will 130. $12 gain $5 in 10 yr.? 138. At what per cent will any sum double itself in 5 yr.? SOLUTION. At 1% any sum will gain 5% in 5 yr. Since to double itself it must gain 100%, the rate must be as many times 1% as 5% is contained times in 100%. Therefore it must be 20%. Find the per cent at which any sum will double itself 139. In 10 yr. 140. In 4 yr. 141. In 8 yr. 142. In 7 yr. 143. In 12 yr. 144. In 100 yr. 145. In 12 yr. 6 mo. 146. In 2 yr. 3 mo. 147. At what per cent will $200 double itself in 4 yr.? 148. At what per cent will $100 double itself in 8 yr.? 149. At what per cent will $150 double itself in 15 yr.? 150. At what per cent will $ 500 treble itself in 16 yr. 8 mo.? 151. At what per cent will $175 quadruple itself in 2 yr. 6 mo. ? 1 PROBLEMS. 122. 1. A's note of $25 has been due 2 years. What the interest, at 6% ? SOLUTION. -The interest for 2 years at 6% is 12% of the ncipal; 12% of $25 = $3. 2. I borrowed $300 for 3 years, at 7%. What will the interest? 3. What is the interest on a note of $46.50, for 5 ars, at 10% ? 4. I owe two notes, one for $145, due in 2 years, at , and the other for $200, due in 3 years, at 6%. ow much interest must I pay on both? 5. A man gave a note for $88.96, due in 4 years, at %. What will be the interest? 5. I gave a note due at date, for $45.50, but did not it until the end of 5 years. y e, at 8% ? What was the interest 7. A rents a store to B for a yearly rent of $360, ich is 12% of the cost. What is the cost? 3. What is the interest on a loan of $1500, made n. 1, 1892, and called in Jan. 1, 1895, if the rate 5%? 9. A man bought 6 horses, for which he paid a sum money which in 2 years 6 months, at 4%, would have -en him $90 interest. How much did he pay for h horse? SOLUTION. -The interest of $1 for 2 years 6 months, at 4%, $.10, and it will take as many dollars to gain $90 as $.10 contained times in $90, which is 900 times. Therefore it will e $900; † of $900 = $150, the price of each horse. 10. A man deposits 3 of his money in the bank, which ngs him an annual income of $1500, at 10%; the aining 4 he invests in business which yields him |