It’s by trial and error and take the most convenient number of u. (There is no correct or wrong number of total “u”, just convenient or inconvenient number of u. See note at end.)

First look is using 8u for Mango so can get 5/8 of Mango. That means Kiwi is 2u and total is 10u. But 10u is not divisible by 3 (1/3 of total). So make total 30u and flow it through the workings.

In fact, I think this is the most tricky part and worth all the efforts to do a quick planning before detailing down the workings. With enough practice like this, it will take less time to plan ahead and also less pain and “smoother” workings without fractional u. Hope it helps.

(Note: any number of total “u” can be used to solve the question. It is just that workings is complicated with fractional u, and easy to get careless with too many fractions)

Just for fun to get the idea…. to demonstrate

Example 1: “Inconvenient” number of units:

Let Total 10p

4/5 is Mango (8p) 1/5 is Kiwi (2p)

sold 5/8 (5p) left 3/8 (3p) sold 125 pc left 2p-125

Left 1/3 of original = 10p/3 = 3p + (2p -125)

1p/3 = 2p-125

125 = 5p/3

25 = p/3 –> p=75

She sold 5p+125 = 375+125= 500 tarts#

Example 2: “VERY Inconvenient” number of units:

Let Total be y

4/5 is Mango (0.8y) 1/5 is Kiwi (0.2y)

sold 5/8 (0.625*0.8y=0.5y) left 3/8 (0.3y) sold 125 pc left 0.2y-125

Left 1/3 of original = y/3 = 0.3y + (0.2y -125)

(x3) y = 0.9y +(0.6y-375)

0.1y = 0.6y – 375

375 = 0.5y –> y=750

She sold 0.5y+125 = 375+125= 500 tarts#