What's the big deal? The big ho-ha is just that now every parents want their kids to score 100/100. That's why every questions count. In the previous generation, who cares. So why the different now? Because every parents are paying so much on tuition fee, so they expect 100% results!!! Haha, perhaps that's the bottom line, and the norm behaviour for parents like us in Singapore.
BTW, IMHO for those parents who have shared their time teaching their kids, than leaving them to the "Professional" or tuition teachers. They will find no problem solving this question also and exactly how it should be done the P6 way. Simultaneous equation is not a preferred method for P6.