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## Wednesday, January 16, 2008

### MGS (Paya Lebar) Pri School P6 Math CA1 2006 (Q37)

I have 38 coins and they are made up of 50-cent and 20-cent coins. Their total value is \$13.60. What is the ratio of the number of 20-cent coins to the number of 50-cent coins?

Solution

Assume all are 20-cent coins

38 coins x \$0.20 = \$7.60

But the total value is \$13.60. This is \$13.60 - \$7.60 = \$6 more, compared to if all 38 coins were 20-cents.

A 50-cent compared to a 20-cent coin has a value that is 30 cents more.

30 cents “more” ---- 1 (50-cent coin in place of a 20-cent coin)

10 cents “more” ----- 1 divided by 3 = 1/3

(\$6) or 600 cents “more” ----- 1/3 x 600 = 20 (50-cent coins)

If there are 20 50-cent coins, it means there are 18 20-cent coins.

Therefore the ratio of 20-cent coins to 50-cent coins is:

Answer: The ratio of the number of 20-cent coins to the number of 50-cent coins is 9:10.