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a) Sam can’t buy more than box of gel pens, since $6.40 x2 = $12.80.
However, he can’t buy only ballpoint pens, since $1.80 x5 = $9.00 only, and $1.80 x6 = $10.80.

So it must be 1 box of gel pens = $6.40, and $3.60 worth of ballpoint pens (2 boxes).

b) For Tom to buy 22 gel pens more than ballpoint pens, he must meet the following conditions:

• number of ballpoints is a multiple of 6

• number of gel pens is a multiple of 4

• difference is 22

• total is between 40 and 60

Trick is to ask how many boxes of gel pens he can buy at most. Max is 9 boxes since 36 + 22 is 58. But 22 not divisible by 6, so it won’t allow him to buy full boxes of ballpoints.
He must therefore buy 8 boxes of gel pens and 2 boxes of ballpoints, since 32+12 is 44.

 

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This kind of reminds me of the chicken and cow legs problem.

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Haha!

As you can see though, my answers are predominantly algorithmic (from my CS background) or they are organic (from my Chemistry background). I always found formal basic algebra terribly boring, so I only learnt as much as I needed to handle sciences. Now however, I’ve discovered that this kind not-so-algebraic working is acceptable to MOE for PSLE! From zero to hero! 😀

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