Katie invested a total of $4000, part at 2% simple interest and part at 3% simple interest. At the end of 1 year, the investments had earned $90 interest. How much was invested at each rate?

$3000

$1000

Step-by-step explanation:

the formula for simple interest = principal x time x interest rate

let the amount invested in the 2% investment be a

let the amount invested in the 3% investment be (4000 - a)

(a x 0.02 x 1) + ([4000 - a] x 0.03 x 1) = $90

0.02a + 120 - 0.03a = 90

Collect like terms and solve for a

0.01a = 30

a = $3000

The amount invested in the 3% investment be (4000 - a)  = $4000 - $3000 = $1000

x = central angle apc = measure of minor arc ac

the two angles x and 30 add to 180, so x+30 = 180 and x = 180-30 = 150. the measure of minor arc ac is 150 degrees.

what we need to do from here is find the circumference and then multiply it by x/360 since there are 360 degrees in a circle. in this case, x = 150, so x/360 = 150/360 = 15/36 = 5/12. the shortest distance along the curve from a to c is 5/12 of the distance around the entire circle (aka circumference)

c = circumference

c = pi*d

c = pi*24

c = 24pi

now multiply this by 5/12 to get

distance along minor arc ac = (5/12)*(circumference)

distance along minor arc ac = (5/12)*(24pi)

distance along minor arc ac = 10pi

the formula you can use is

l = (x/360)*pi*d

with

l = length of minor arc

x = central angle

d = diameter

which essentially is the steps we took though a bit differently.