Maths Question below! Must do working.?

Question

Penny had twenty 50cent and 20cent coins in her piggy bank. The total value of the coins was $6.40. How many 20cent coins did she have?

Answer 1

£1.50

Answer 2

Ans :

Let Number 50cent coins be x and
Number of 20cents coin be y

x + y = Total number of coins
x + y = 20
y = 20 - x ..................... (Eqn 1)


Since x numbers of 50 cents coin and y numbers of 20cents coin total to $6.40 (640 cents)

50x + 20y = 640 ...............( Eqn 2)
Substituting x = 20 - y into Eqn 2

50x + 20(20-x) = 640
50x + 400-20x = 640
50x - 20x = 640 - 400
30x = 240
x = 8

Substituting x= 8 into Eqn1

y = 20 - 8
y = 12

Therefore she have 12 twenty cent coins.

Proof.

12 * $0.20 = $2.40 (Total amount for 20cents coin)

8 * $0.50 = $4.00 (Total amount for 50 cents coin)

Total amount she had = $2.40 + $4.00 = $6.40 (Proved)

Therefore answer is she had 12 twenty cent coins.


hope you understand.

Cheers.

Answer 3

12

make two equations and solve by substituion or adding or subtracting them

50X + 20Y= 640 or .5X + .2Y= 6.40
X + Y= 20

mutiply the bottom eqn by 50 then subtract

-30Y = -360

divide by -30
You get Y=12 or 12 20cent coins

Answer 4

50X + 20Y= 640
=> 0.5X + 0.2Y= 6.40
and
X + Y= 20................(2)

mutiply the equation (1) by 50 then subtract

-30Y = -360

divide by -30

Y=12 or 12 20cent coins

Answer 5

8 x 50 = $4.00 12 X 20 = $2.40

Answer 6

its very easy asking people to do your homework...this is lame. stop surfing the Internet and read up your text.
Homework help is fine, and people are generally nice to give a helping hand, but it always easier to have someone give you a fish, then you learning to fish.
If you try, and it turn out to be wrong. But you tried, and at the same time you learn to learn.

Answer 7

20x+50y=640
x+y=20
solving 20x+20y=400
30y=240
y=8
so 12nos 20 cent coins