Last updated at Dec. 8, 2016 by Teachoo

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Ex 3.2, 19 A trust fund has Rs 30,000 that must be invested in two different types of bonds. The first bond pays 5% interest per year, and the second bond pays 7% interest per year. Using matrix multiplication, determine how to divide Rs 30,000 among the two types of bonds. If the trust fund must obtain an annual total interest of: Rs 1,800 (b) Rs 2000 Let. Investment on 1st bond. = Rs x So investment on 2nd bond = Rs 30,000 x We represent investment per bond by matrix A Let A = [ 8( @30,000 )] The first bond pays 5% interest per year & The second bond pays 7% interest per year We represent interest per yer per bond by matrix B Let B = [ 8(5%& 7%)] = [5/100 7/100] Now, Total Annual Interest = Interest per bond Investment per bond = BA = [5/100 7/100]_(1 2) [ 8( @30,000 )]_(2 1) = [5/100 " + " 7/100 " (30,000 " ") " ]_(1 1) = 5/100 + 7/100 (30000 ) Now in part (a) Total annual interest = Rs 1800 5/100 + 7/100 (30000 ) = 1800 5 /100 + (7 (30000 ) )/100 = 1800 (5 + 7(30000 ))/100 = 1800 5x + 7 (30000 x) = 1800 100 5x + 210000 7x = 180000 5x 7x = 180000 210000 2x = 30000 x = ( 30,000)/( 2) x = 15,000 So amount investment at 5% = x = Rs. 15,000 & amount investment at 7% = Rs (30,000 x) = Rs. (30,000 15000 ) = Rs 15,000 Now in part (b) Total annual interest = Rs 2000 5/100 + 7/100 (30000 ) = 2000 5 /100 + (7 (30000 ) )/100 = 2000 (5 + 7(30000 ))/100 = 2000 5x + 7 (30000 x) = 2000 100 5x + 210000 7x = 200000 5x 7x = 200000 210000 2x = 10000 x = ( 10,000)/( 2) x = 5,000 So amount investment at 5% = x = Rs. 5,000 & amount investment at 7% = Rs (30,000 x) = Rs. (30,000 5000 ) = Rs 25,000

Ex 3.2

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Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.