Question

a trust has rupees thirty thousand it is invested in two different types of bonds. the first bond pays five percent interest per annum which will be given to the orphanage and second bond pays seven percent per annum which will be given to N.G.O for cancer aid. trust obtains an interest of rupees one thousand eight hundred. how much amount is invested  in each type of trust?

Answer 1

Formula:
principal amount = p
rate per annum = r%
time = t
interest = (p * r * t) / 100

Now say x is invested in first type of bond and y is invested in second type of bond

So,
x + y = 30000...........(1)

Now interest for first type of bond = (x * 5 * 1) / 100
And interest for second type of bond = (y * 7 * 1) / 100
So, total interest = (5x + 7y) / 100
And, (5x + 7y) / 100 = 1800
⇒ 5x + 7y = 180000.......(2)

Multiply by 5 in eq(1)
5x + 5y = 150000.......(3)

eq(2) - eq(3)
2y = 30000
⇒ y = 15000

from eq(1)
x = 30000 - y
x = 30000 - 15000
⇒ x = 15000


Answer
Fifteen thousands in both type of bonds

Answer 2

Amount in first bond = Rs X        Amount in 2nd Bond = Rs (30,000 - X)

Interest per year  from 1st Bond : 5 X /100  Rs
Interest per year from 2nd bond :
    $(30000 - X) 7/100 = (2100 - 7X/100)  Rs$

Sum of interests =
$5X/100 + 2100 - 7 X/100 = 1800 \\ -2X/100 + 2100 = 1800 \\ X/50 = 300 \\ X = 15000$

Amount invested in Ist bond/trust as well as 2nd bond/trust = Rs 15,000