The blog postings are about the Singapore Math. The readers can learn from the postings on Solving Singapore Primary School Mathematics. You or your kids can learn dealing with Math modeling, Problem Sum from Lower Primary School to Upper Primary School level in Singapore school. This posting is a primary school math question on Ratio, Fraction and Problem sum.

You can read posting **Sarin and his coin bank** on the story of coin bank.

Read also posting on **Sarin and the million numbers** to understand concept of dollars and cents.

Read also the posting on **Sarin learns concept of ratio in school **to understand the concept of Ratio. Read also the posting on **Sarin learns the concept of Fraction (mathematics concept)** to know about the concept of Fraction.

Upper primary school mathematics question UPQ182

Sarin had some 20-cent and 50-cent coins in his coin bank. 7/8 of the coins were 20-cent coins and the rest were 50-cent coins. After Sarin withdrew $72.50 worth of 50-cent coins and 5/7 of the 20-cent coins from the coin bank, he had 2/7 of the coins left. Find the total amount of money Sarin left in the coin bank.

Solution:

The number of 50-cent coins spent = 72.50 ÷ 0.5 = 145

The ratio of number of 20-cent to 50-cent = 7 : 1

Draw the math model

From the model

5 units = 145

1 unit = 29 coins

Number of 20-cent coins left = 14 × 29 = 406

Value of 20-cent coins left = 406 × 0.2 = $81.20

Number of 50-cent coins left = 2 × 29 = 58

Value of 50-cent coins left = 58 × 0.5 = $29.00

Total amount of money Varsha left = 81.200 + 29.00 = $111.20

Alternative solution:

The ratio in the coins bank 20-cents : 50-cents : all = 7 : 1 : 8 = 49 : 7 : 56

After withdrew 5/7 of 20-cent

The ratio of 20-cents : 50cents : all = 2 : 1 : 8 = 14 : 7 : 56

Finally left with 2/7 of coins

Finally, ratio of 20-cents + 50-cents : all = 2 : 7 = 16 : 56

Final ratio of 20-cents : 50-cents : all = 14 : 2 : 56

Spent $72.50 of 50-cent

7 – 2 = 5units = 145

1 unit = 29 coins

Number of 20-cent coins left = 14 × 29 = 406

Value of 20-cent coins left = 406 × 0.2 = $81.20

Number of 50-cent coins left = 2 × 29 = 58

Value of 50-cent coins left = 58 × 0.5 = $29.00

Total amount of money Varsha left = 81.200 + 29.00 = $111.20