Q&A - P4 Math

[smartmummy]

htn:

need help for the following:


1) what is the difference between the 5th multiple of 8 and the sum of all the factors of 25?

2) Gina had 12 more fifty-cent coins than one-dollar coins. When she exchanged all of the fifty-cent coins for one-dollar coins, she had 18 one-dollar coins altogether. How many fifty-cent coins did she have?

TIA

1) 5th multiple of 8 = 40
sum of all the factors of 25=25+1+5=31
difference 40-31=9
2)ans is 20....couldn't go down to write as using iphone.
fifty-cent [ u |12 ]
one doll [ u]
(u+12)/2+u=18
u+12+2u=36
u=8

[MathIzzzFun]

htn:

need help for the following:


1) what is the difference between the 5th multiple of 8 and the sum of all the factors of 25?

2) Gina had 12 more fifty-cent coins than one-dollar coins. When she exchanged all of the fifty-cent coins for one-dollar coins, she had 18 one-dollar coins altogether. How many fifty-cent coins did she have?

TIA

1)
5th multiple of 8 --> 40
factors of 25 --> 1,5,25 --- total 31
(3 factors only. All square numbers have odd number of factors because one of the factors has a twin)

40-31=9

2) total amount = $18
12 more fifty cents coins --> $6
$18-$6 = $12 --- removing the excess 50-cents so that there are equal number of $1 and 50-cent coins,
$12 / (1+0.50) = 8

number of $1 coins = 8
number of 50-cent coins = 8 + 12 = 20

cheers.

[lotto]

htn:

need help for the following:


1) what is the difference between the 5th multiple of 8 and the sum of all the factors of 25?

2) Gina had 12 more fifty-cent coins than one-dollar coins. When she exchanged all of the fifty-cent coins for one-dollar coins, she had 18 one-dollar coins altogether. How many fifty-cent coins did she have?

TIA

1) 5th multiple of 8 is 5 x 8 = 40
factors of 25 is 1, 5 and 25. so the sum of all factors is 1 + 5 + 25 = 31
difference is 40 - 31 = 9

2) the easiest method to undestand is this assumption i think. or maybe u can try to draw the model
assume the no. of $1 is 2 units.
So the no. of 50cents is 2 units + 12
When u change all the 50 cents to $1, the no. of $1 u will get is 1 unit + 6 (which is half of 2 units + 12)
Total number of $1 u have now is 2 units + 1 unit + 6 = 3 units + 6
3 units + 6 = 12
3 units = 6
1 unit = 2
50-cents = 2 units + 12 = 16 coins

hope it helps :roll:

[ruohoo97]

smartmummy:

hi ruohoo97!

pls check ur calculation....
9b=72*2
1b=8*2
i think u missed multiply by2?

Yes, smartmummy, you are absolutely right!

[BigDevil]

lotto:

htn:

2) Gina had 12 more fifty-cent coins than one-dollar coins. When she exchanged all of the fifty-cent coins for one-dollar coins, she had 18 one-dollar coins altogether. How many fifty-cent coins did she have?

TIA

3 units + 6 = 12
3 units = 6
1 unit = 2
50-cents = 2 units + 12 = 16 coins

Think it should be
3 units + 6 = 18

since Gina had 18 one-dollar coins after exchanging all the 50-cent coins?

[ssmummy]

Use guess and check method in a table format


The difference between the 50 cents coin and $1 coin is always 12 pieces

50 cents coins $1 coin Is the total equal to $18?
12 pieces 0 piece. No ($6)
13 pieces. 1 piece. No. ($6.50 + $1 = $7.50)
16 pieces. 4 pieces. No ($8 + $4 = $12)
20 pieces. 8 pieces. Yes ($10 + $8 = $18)

There are 20 pieces of 50 cents coin

[htn]

Hi, smartmummy,MathIzzzFun, lotto, BigDevil


Thanks

[lotto]

BigDevil:

lotto:

[quote=\"htn\"]
2) Gina had 12 more fifty-cent coins than one-dollar coins. When she exchanged all of the fifty-cent coins for one-dollar coins, she had 18 one-dollar coins altogether. How many fifty-cent coins did she have?

TIA

3 units + 6 = 12
3 units = 6
1 unit = 2
50-cents = 2 units + 12 = 16 coins

Think it should be
3 units + 6 = 18

since Gina had 18 one-dollar coins after exchanging all the 50-cent coins?[/quote]
Oops... u are right BigDevil.
That's why I always get 99 or 98 for my math paper because of this kind of thing

ssmummy:

Use guess and check method in a table format

The difference between the 50 cents coin and $1 coin is always 12 pieces

50 cents coins $1 coin Is the total equal to $18?
12 pieces 0 piece. No ($6)
13 pieces. 1 piece. No. ($6.50 + $1 = $7.50)
16 pieces. 4 pieces. No ($8 + $4 = $12)
20 pieces. 8 pieces. Yes ($10 + $8 = $18)

There are 20 pieces of 50 cents coin

this guess n check method is also good :goodpost:

[elisammom]

Hi,

Doreen has ome $5 and %10 notes. The notes add up to $470 in total. There are four more $5 notes than $10 notes. How many $5 notes does Doreen have?

solution:
5x4 = 20
470-20 =450
450/15 = 30
30+4 = 34

Pls advise, why 30 + 4 is equal to nos of $5 notes?

Thanks.

[MathIzzzFun]

elisammom:

Hi,

Doreen has ome $5 and %10 notes. The notes add up to $470 in total. There are four more $5 notes than $10 notes. How many $5 notes does Doreen have?

solution:
5x4 = 20
470-20 =450
450/15 = 30
30+4 = 34

Pls advise, why 30 + 4 is equal to nos of $5 notes?

Thanks.

When you remove the 4 extra $5 notes, there will be equal number of $5 and $10 left with total amount = $470-$20 = $450

one group of (1x$5 note+ 1X$10 note) = $15
$450 / $15 = 30 groups
there is 1x$5 note in one group and 4x$5 was removed first,
so total number of $5 notes = 30 x 1 + 4 = 34

cheers.