Q&A - P3 Math

[bbc]

Robin has 4 times as many marbles as Sam.

After Sam buys another 105 marbles, he has twice as many marbles as Robin. How many marbles does Robin have?

[PapayaDad]

bbc:

Hi,

Pls help with the following. thanks.

Lily had $61 in two-dollar notes and five-dollar notes.
She had 20 notes altogether.
She used all her five-dollar notes to buy a bag.
How much did the bag cost?

Assume 10 $2 and 10 $5
20 + 50 = 70
Too much, need to reduce $9

If we reduce 1 x $5 = -$5
But $2 will increase by 1 = +$2
The result is $3 reduce.
So we need to reduct 3 x $5 ; which means 13 $2 and 7 $5
26 + 35 = 61 correct

Bag cost $35

[PapayaDad]

bbc:

Robin has 4 times as many marbles as Sam.

After Sam buys another 105 marbles, he has twice as many marbles as Robin. How many marbles does Robin have?

At first :

R:UUUU
S:U

Then S buy 105 ie. (U+105)

R:UUUU
S:UUUUUUUU

So

8U = U + 105
7U = 105
U = 15

R = 4U = 60

[PapayaDad]

bbc:

Jeric had 45 marbles more than Mark. After Jeric lost 75 marbles, Mark had thrice as many marbles as what Jeric had left. How many marbles did Jeric have at first?

In the end :

M:UUU
J:U

at first (j not yet lost 75)

M:UUU
J:U +75 = 45 more than Mark = UUU + 45

U+75 = UUU + 45
2U = 30
U = 15

At first J have U+75 = 15 + 75 = 90
Mark have 3U = 3 x 15 = 45

Check J lost 75 = 15 ; Mark have 3 times more = 45. correct

[bbc]

Thanks, PapayaDad.

[vinegar]

Mary thinks of a 2-digit number.When the number is divided by 5, the remainder is 3.When the number is divided by 9, th remainder is 1. What is the number?

[vinegar]

Ali has 318 story books. If she wants to donate 7 story books to each of her students, what is the maximum number of students she can donate to?

[sembgal]

318 divided by 7= quotient and remainder.

Quotient: 45. The answer for number of students
Remainder = 3. The answer for remaining books.
Take the quotient as the answer.

[sembgal]

vinegar:

Mary thinks of a 2-digit number.When the number is divided by 5, the remainder is 3.When the number is divided by 9, th remainder is 1. What is the number?

The answer is 40.
Working: 5 + 3 = 8
9 + 1 =10
The first common multiple of 8 and 10 is 40
8, 16, 24, 33, 40
10, 20, 30, 40

[ammonite]

sembgal:

vinegar:

Mary thinks of a 2-digit number.When the number is divided by 5, the remainder is 3.When the number is divided by 9, th remainder is 1. What is the number?

The answer is 40.
Working: 5 + 3 = 8
9 + 1 =10
The first common multiple of 8 and 10 is 40
8, 16, 24, 33, 40
10, 20, 30, 40

? 40 divided by 5 is 8, no remainder leh.

I don't know what the standard method is, but through deduction, my answer is 28.