Maths tip:

Qn: Kenny and Joo Seng are selling durians at a fruit stall.

If Kenny sells 60 durians per day and Joo Seng sells 15 durians per day, Kenny will have 24 durians left when Joo Seng has sold all his durians. If Joo Seng sells 60 durians per day and Kenny sells 15 durians per day, Kenny will have 204 durians left when Joo Seng has sold all his durians. How many durians does Kenny have?

Solution tips:

1. Recognise this is a two scenario type question. If <change A> then <result A>, if <change B> then <result B>.

2. try to equate A and B together by noticing that the before change condition is the same in both.

3. try to determine what you can from the information given.

In this example:

Notice that the number of durians that Kenny has is the same in both scenarios – we will try to equate that.

i.e. 24+60 * (days in first) = 204 + 15 * (days in second)

We know that Joo Seng sells his durians in 1/4 of the time in the second instance compared to the first instance (he sells 60/day rather than 15/day).

i.e. number of days taken in the first scenario = D

number of days taken in the second scenario = D/4

Therefore,

24+60D = 204 + 15 D/4

56 1/4 D = 180

D = 3.2

So Kenny has 60D+24 = 216 durians. (qn a)

Joo Seng has 15*3.2 = 48 durians. total sold for = (216+48)/4*10=$660 (qn b)