Ratio, maths homework :(?

Question

Can anyone help me? :(

Maria, Carolina, and Pedro receive $800 from their grandmother in the ratio

Maria: Carolina: Pedro = 7:5:4.

(a). Calculate how much money each receives.

(b). Maria spends 2/7 of her money and then invents the rest for two years at 5% per year simple interest.

How much money does Maria have at the end of the two years?

(c). Carolina spends all of her money on a hi-fi set and two years later sells it at a loss of 20%.

How much money does Carolina have at the end of two years?

(d). Pedro spends some of his money and at the end of the two years he has $100.

Write down and simplify the ratio of the amounts of money Maria, Carolina, and Pedro have at the end of the two years.

(e). Pedro invents his $100 for two years at a rate of 5% per year compound interest. Calculate how much money he has at the end of these two years.

Answer 1

(a)  When you're dealing with ratios, there's always a constant involved:  the ratio between two corresponding things will always be that constant. In this problem, let the constant be k.  The fact that the money comes in the ratio 7:5:4 and the total is $800 means

7k + 5k + 4k = 800

16k = 800

k = 800/16 = 50

So Maria gets 7(50) = 350, Carolina gets 5(50) = 250, and Pedro gets 4(50) = 200.  350 + 250 + 200 = 800.  This process will always work.

Given that, the rest of the problems shouldn't be that hard, so I'll let you tackle them.