Let's have a variable for each rate
x = account 1 (2.5% rate of interest)
y = account 2 (8% rate of interest)
The formulas we need are:
0.025x + 0.08y = 830 (amount of interest paid)
x + y = 20 000 (combined amount invested)
To solve we will use substitution (isolate for one variable and plugging into the other formula):
x + y = 20 000
x = 20 000-y
0.025x + 0.08y = 830
0.025(20 000-y) + 0.08y = 830
500-0.025y+0.08y=830
500+0.055y=830
0.055y=330
y=6000
Now that we know y (the 2nd account) = $6000 we need to find x. We do this by using the previous formula.
x = 20 000-y
x=20 000 - 6000
x=14000
She invested $14 000 at a 2.5% interest rate and $6 000 at a 8% interest rate.
*Notes:
the percentages were converted into decimal form
you check your answer by plugging the numbers back into the 2 formulas we made
Its 80 because if you find perfect square around the number 80 you'd get
√64 and √81
which would be 8 and 9
