Question

suppose you have 12000 rupees to save. You have to save some amount at 10% and at reast at 15%.How much should be saved at each rate to yield 12% on total amount?????

Answer 1

x=invested at 10%
12000-x=invested at 15% 
.10x+ (.15)(12000-x)=1440 ;; 12% of the total amount is 12% of $12000. 
.10x + 1800-.15x=1440
-0.05x=-360
x=7200 
12000-x=4800 
$7200 at 10%=$720
$4800 at 15%=$720 
That is $12000 earning $1440, and that is 12% 

Answer 2

Answer:

Let x be the which is saved in the interest of 10%,

⇒ The remaining which is saved in the interest of 15% = ( 12000 - x )

The total interest = The interest on the amount of x + The interest on the amount of (12000 - x)

= $\frac{x\times 10}{100}+\frac{(12000-x)\times 15}{100}$

According to the question,

The total interest = 12 % of 12000 = 0.12 of 12000 = 1440

⇒  $\frac{x\times 10}{100}+\frac{(12000-x)\times 15}{100}=1440$

⇒$10x+(12000-x)15=144000$

⇒ $-5x+180000=144000$

⇒ $180000-144000 = 5x$

$\implies 5x = 36000\implies x = 7200$

Thus, the amount invested at the interest of 10% = x = 7200 rupees

And, the amount invested at the interest of 15% = 12000 - 7200 = 4800 rupees.