At a doughnut shop, one order of 4 coffees and 7 doughnuts costs $3.90. If another order of 6 coffees and 3 doughnuts costs $3.60, find the cost of one coffee.
Is ist a proportion problem? How do I set it up and solve it?
2006-12-03 01:55:12 · 7 answers · asked by Robyn & L 1 in Science & Mathematics ➔ Mathematics
assume 'x' for coffee and 'y' for doughnut
Then the problem statement is as follows:
Statement1: 4x + 7y = 3.9
Statement2: 6x + 3y = 3.6
Multiply Statement 1 by 3 & Multiply Statement 2 by 7
New Statement1: 12x + 21y = 11.7
New Statement2: 42x + 21y = 25.2
Now, New Statement2 minus New Statement1:
Result: 30x = 13.5
Therefore, x = 13.5/30 = 0.45
x = 1 coffee = $0.45
Phew !!
2006-12-03 02:14:34 · answer #1 · answered by Octy a.k.a Octane★97 5 · 0⤊ 0⤋
okkkk, so heres the clostest I got, try,
4\7 divided into 3.90\1..... you know how to work that right? Well, divide the seven into the 15.60 (thats what I got from working the division prob) and then take that answer, because that's the cost of the doughnuts, I got $2.22. Then divide 4 into $2.22..... I got.. or should I tell you? LOL! What ever, the answer I got would be that one coffee cost, 42 cents.
What grade are you? Anyway, hope that helps.....
EDIT:
Wait a minute! I just ran this question by some of my family and their trying to figure it out but my mo keeps yelling that 'how on earth can you figure out the price of a coffee if you didn't no the price of the doughnuts???" And yeah, I wonder too! LOL! and I redid the prob and came out with $2.23 instead of $2.22....
2006-12-03 10:06:20 · answer #2 · answered by JoGirl 2 · 0⤊ 0⤋
Ok let x = the cost of the coffee
since there are 2 problems we set up two equations and solve for x.
1) 4x - 7 = 3.90
2) 3x - 3 = 3.60
You will note that I changed the sign of 3 and 7 because otherwise you'd get a very irrational numbers for x.
Work each problem the way you would for any algebra problem I will work problem 2 for you.
3x - 3 = 3.60
+3 = +3
3x = 6.60
/3 = /3
x = 2.20
2006-12-03 10:34:37 · answer #3 · answered by ikeman32 6 · 0⤊ 0⤋
Set up two equations
Eq1 4c + 7d =3.9
Eq2 6c + 3d =3.6
Then solve for c - coffee and d doughnut
Multiply Eq1 by 6 and Eq2 by 4
We have
Eq1 24c + 42d =23.4
Eq2 24c + 12d =14.4
Eq1 – Eq2=30d=9
Then d = 9/30=.3 ($0.30) or 30 cents (very cheap, almost 1970’s prices)
We have to find C
From Eq1 4c +7(.3)=3.9
c=(3.9-2.1)/4=
c=1.8/4=.45 or $0.45
2006-12-03 10:02:53 · answer #4 · answered by Edward 7 · 0⤊ 0⤋
I am not sure it will come under proportion. Form the equations like
4c+7d = 3.90 &
6c+3d = 3.60
Solve the two equations and obtain the value of c which will give you the price of one coffee.
2006-12-03 10:05:26 · answer #5 · answered by tBone 5 · 0⤊ 0⤋
coffee = c
doughnuts =d
4c+7d=3.9
ie 12c+21d=11.7
6c+3d=3.6
ie 42c+21d=25.2
ie 30c=13.5
ie c=0.45
price of coffee is $0.45
2006-12-03 10:09:48 · answer #6 · answered by Adi 2 · 0⤊ 0⤋
cost of one coffee is $0.45
4c = 3.9 - 7d
c = (3.9/4) - (7/4) d
6((3.9/4) - (7/4 )d) + 3d = 3.6
3d - 10.5d = 3.6 - 5.85
- 7.5d = -2.25
d = 0.3
c = 0.45
2006-12-03 10:08:13 · answer #7 · answered by tulip 2 · 0⤊ 0⤋