Math Questions?

Question

How to solve these questions? I need formulae for colege entrance exams..:D

The sales price of a car is $12,590, which is 20% off the original price. What is the original price?

If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

Answer 1

Q1.)$12,590 = 80% of original value. (100%-20%)
($12,590/80)*100=157.375*100
=$15,737.50(100%)


Q2.)We know that Sally can paint the house by herself in four hours. Put another way, she can paint 1/4 of the house in an hour. Using similar logic, we know John paints at a rate of just 1/6 of a house per hour. If we convert those fractions to fractions with a common denominator, we have 3/12 of a house for Sally and 2/12 of a house for John, so together they can paint at a rate of 5/12 of a house per hour.

But that is not yet the answer to the question.

If you take the reciprocal of 5/12 houses per hour, you get 12/5 hours per house. That equals 2.4 hours per house. Converting to hours and minutes, you get 2 hours, 24 minutes -- because 0.4 hours equals 24 minutes. (0.4 hours x 60 minutes/hour = 24 minutes.)

Answer 2

1.) 100% - 20% = 80% = 0.8
12590 = 0.8X
X = 12590/0.8 = $15737.50
2.) Sally can paint 1/4th of the house in one hour.
John can paint 1/6th of the house in one hour.
Let X be the number of hours required to paint the house working together.
Then:
(1/4)X + (1/6)X = 1 ...(One whole house)
Multiply both sides by the LCD:
6X + 4X = 24
10 X = 24
X = 2.4 hours

Answer 3

let x the original price
$12,590 = x(1 + .2)
x = $10491.67

let x number of hours for both person to paint the house
x/4 + x / 6 =1
6x + 4x = 24
x = 2.4 hours

Answer 4

Hello Steffi...if the sale price is 12590 =20percent ,divide 12590 by 20 to get 1percent then multiply by 100 to get 100 percent..Her I'll do it for you. 12590/20=629.50 so 100 x 629.50= 62950.00
on the second question I'll give you a hint ....the two working together can do it faster than either working alone
time to do job= t(job/4hrs) + t(job/6hrs)
t=1/4+1/6 total job hours
lowest com mom multiple=12
1job=t(3/12job/hour + 2/12job/hour)
combine like terms
1job=t(5/12job/hour)
solve for t
dint forget to invert
t=1job/1 x 12/5
t=12/5
t=2.4 hours
basically this is it...get the whole job equal to the parts then ya got it...Oh yea .4 hours is what? .4 x 60 = 24 minutes...good luck from the E....
total=5/12 =