Decimal P5

Each day, Mike saves $0.50 while Carol saves $0.30 more than her. Carol starts saving 6 days after Mike. She has $17.40 more than Mike now. How much does Mike save now?


0.50 x 6 = $3.00            Amount saved by Mike in first 6 days

3.00 + 17.40 = $20.40   Additional amount saved by Carol

20.40 ÷ 0.30 = 68 days  Number of days Carol took to save $20.40 more

68 + 6 = 74 days            Total number of days Mike saved

74 x 0.50 = $37

Mike saves $37 now

Decimal P5

7. Mrs Smith bought some mangoes and mangosteens for $16.50. She bought 5 fewer mangoes than mangosteens. Each mango cost $1.80 more than each mangosteen. How many mangosteens did she buy?

Mangoes        Mangosteens

---------------------------                           

     1                    6             

16.50 – 1.80 = 14.70

14.70 ÷ 7 = 2.10

Check

------

1 x (2.10 + 1.80) + 6 x 2.10 = $16.50

He bought 6 mangosteens.

     5                  10

5 x 1.80 = 9

16.50 – 9 = 7.50

7.50 ÷ 15 = 0.50

Check

-------

5 x (0.50 + 1.80) + 10 x 0.50 = $16.50

He bought 10 mangosteens.

Decimal P5 2009 SA1 P2 MGS Q13

13. Arnold has some 50-cent coins and Weili has some 20-cent coins. Arnold has 5 fewer coins than Weili. However, the amount of money Arnold has is $2.60 more than the amount of money Weili has. [P5 2009 SA1 P2 MGS Q13]

a) How much money does Arnold have? [3]

b) How many 20-cent coins does Weili have? [1]

Arnold has 5 fewer coins than Weili. However, the amount of money Arnold has is $2.60 more than the amount of money Weili has.

Given the above information, we need to remove the 5 additional 20-cent coins to make the number of 20-cent and 50-cent coins the same, so as to group them as a set.

5 x $0.20 = $1.00

By removing the 5 additional 20-cent coins, the difference in value between the 20-cent coins and 50-cent coins will increase.

1.00 + 2.60 = $3.60

With the total difference in value and the 1-to-1 difference, we will be able to find the number of sets.

0.50 – 0.20 = $0.30

3.60 ÷ 0.30 = 12 sets

12 x 0.50 = $6.00

a) Arnold has $6.00.

To get the number of 20-cent coins, we need to put back the 5 20-cent coins removed from the sets.

12 + 5 = 17 20-cent coins

b) Weili has 17 20-cent coins.

Alternative method:

5 x 0.20 = $1.00

Number

W 20¢ [1 u ][5]

A  50¢ [1 u ]

-------------------

Amount

W 20¢ [ 10 u ][ 10 u ][100]<       260        >

A  50¢ [         ][         ][         ][         ][         ]

30 u -- > 100 + 260

1 u -- > 360 ÷ 30 = 12

A 50¢ -- > 12 x 50 = 600¢

                              = $6.00

a) Arnold has $6.00.

W 20¢ -- > 12 + 5 = 17 20¢ coins

b) Weili has 17 20-cent coins.