Answer:
Let 
and 
.
a)
b)
c) Now we calculate the direction of 
and 
We calculate the direction of like this:
. Since, 
, then the direction of is 
.
Now, for
.
Given:
Total amount invested = $9,000
interest rates = 4% and 6%
Let x be the part of 9,000.
Note that annual return on each investment is the same.
0.04x = 0.06(9,000 - x)
0.04x = 540 - 0.06x
0.04x + 0.06x = 540
0.10x = 540
x = 540/0.10
x = 5,400
0.04x = 0.06(9,000 - x)
0.04(5,400) = 0.06(9,000 - 5,400)
216 = 0.06(3,600)
216 = 216
total interest for the year : 216 + 216 = 432
Interest = pricipal * interest rate * term
432 = 9,000 * interest rate * 1 yr
432/9,000 = interest rate
0.048 = interest rate
Interest rate would be 4.8% to get the same interest from the whole 9,000.
X jumpers at <span>£15 each. Total = 15*x = </span><span>£15x
</span>
y shirts at £12 each. Total = 12*y = <span>£12y
Total cost = </span><span>£15x + </span><span>£12y
Total cost = </span><span><span>£(15x + 12y)</span></span>
