# Math 11 questions!!! help?

The answer is written down. So I am looking for a shown work..

Thanks

1) If a two place # is divided by the sum of its digits the quotient is 8, and the difference between its digits is 5. Find this number..

ANSWER = 72

2) Mac invested $1200, part at 8% and the rest at 6% per year. The interest earned after one year was $88. How much did Mac invest at each rate?

ANSWER = $400 at 6%, 800 at 8%

3) A boat can make a trip up river 60km to a fish camp in 3 hours, and down the river to its starting point in 2hours. If the boat can travel x km/hr in still water and the speed of the current is y km/hr,

Find x and y...

ANSWER: x = 25, y = 5

4) Solve

3a + 4B - c = -2

2a - 3b + c = 4

a - 6b + 2c = 5

ANSWER: (1, -3, -7 )

5) If (a,b,1) is a solution for the system

x + y - 2z = 1

2x - 2y + z= -1

kx - y - z = 2

ANSWER: a= 1, b = 2, k = 5.

Help me answer all the questions.

But if you can answer atleast 1 or 2, please share the shown work =]

Just need it for a review.

2 & 3 is answered by Lucy << thanks..

Can someone help me with 1, 4, 5?

### 2 Answers

- LucyLv 71 decade agoFavorite Answer
2) Mac invested $1200, part at 8% and the rest at 6% per year. The interest earned after one year was $88. How much did Mac invest at each rate?

ANSWER = $400 at 6%, 800 at 8%

This is a type of mixture problem.

Hint: Use a table.

Type ….........………. Qty …………. Interest …………. Total

8% account …………. x …...………. 0.08 ……....……. x * 0.08 = 0.08x

6% account …………. y ……...……. 0.06 …....………. y * 0.06 = 0.06y

Total ………..........…. x + y ………. ----- ……......……. 88

The first 2 rows of the last column always add up to the third row in that column.

0.08x + 0.06y = 88

Given: Combination is 1200 dollars

Means: x + y = 1200

You now have 2 equations.

0.08x + 0.06y = 88

x + y = 1200

Solve the 2nd one for x.

x + y = 1200

x = 1200 - y

Replace x with 1200 - y in the 1st one.

0.08x + 0.06y = 88

0.08(1200 - y) + 0.06y = 88

96 - 0.08y + 0.06y = 88

-0.02y = -8

y = 400

Plug this solved y value into x = 1200 - y to solve for x.

x = 1200 - y

x = 1200 - 400

x = 800

~~~~~~~~~~~~

3) A boat can make a trip up river 60km to a fish camp in 3 hours, and down the river to its starting point in 2hours. If the boat can travel x km/hr in still water and the speed of the current is y km/hr,

Find x and y...

ANSWER: x = 25, y = 5

Hint: Use a table.

________________ Distance ______________ Rate _____________ Time

Upstream ________ 60 ___________________ x - y _____________ 3

Downstream ______ 60 ___________________ x + y ____________ 2

Remember the distance formula.

d = rt

Apply this to what you have.

________________ Distance ______________ Rate _____________ Time

Upstream ________ 60 = 3(x - y) __________ x - y _____________ 3

Downstream ______ 60 = 2(x + y) __________ x + y ____________ 2

Your system of equations is:

60 = 3(x - y)

60 = 2(x + y)

Solve the first equation for x.

60 = 3(x - y)

60 = 3(x) + 3(-y)

60 = 3x - 3y

60 + 3y = 3x - 3y + 3y

60 + 3y = 3x

(60 + 3y) / 3 = 3x / 3

(60 / 3) + (3y / 3) = x

20 + y = x

Plug this into the second equation and solve for y.

60 = 2(x + y)

60 = 2(20 + y + y)

60 = 2(20 + 2y)

60 = 2(20) + 2(2y)

60 = 40 + 4y

60 - 40 = 40 + 4y - 4

20 = 4y

20 / 4 = 4y / 4

5 = y

Plug this back into the modified first equation to find x.

20 + y = x

20 + 5 = x

25 = x

ANSWER: The speed of the boat in still water is 25 km/h. The speed of the current is 5 km/h.

Source(s): For more help with mixture word problems: http://www.purplemath.com/modules/mixture.htm For more help with distance word problems: http://www.purplemath.com/modules/distance.htm