Gmat_mission wrote: ↑

Sun Jun 21, 2020 3:41 pm

Barbara invests $2400 in the National Bank at 5%. How much additional money must she invest at 8% so that the total annual income will be equal to 6% of her entire investment?

A. 1200
B. 3000
C. 1000
D. 3600
E. 2400

[spoiler]OA=A[/spoiler]

Source: GMAT Paper Tests

Barbara invests $2400 in the National Bank at 5%.
So, her annual income for this investment = 5% of $2400 = $120
Let x = the additional money Barbara must invest at 8%
So, her annual income for this investment = 8% of x = 0.08x
So, Barbara's TOTAL annual income = $120 + 0.08x

We want the TOTAL annual income to be equal to 6% of her entire investment.
The TOTAL amount invested = $2400 + x
So, we want her TOTAL annual income to equal 6% of ($2400 + x)
In other words, we want: Barbara's TOTAL annual income = 0.06($2400 + x)

We now have the equation: $120 + 0.08x = 0.06($2400 + x)
Expand right side: 120 + 0.08x = 144 + 0.06x
Subtract 0.06x from both sides to get: 120 + 0.02x = 144
Subtract 120 from both sides to get: 0.02x = 24
Solve: x = 24/0.02 = 2400/2 = 1200

Answer: A

Cheers,
Brent