Gap Units Concept (Rift Unit)

First
Darren bought some tarts for a party. 40% of them were strawberry tarts and the rest were chocolate tarts. Each strawberry tart cost $2. The price of each chocolate tart was 90% of the price of each strawberry tart. Darren spent $30.80 more on chocolate tarts than he did on strawberry tarts. How many tarts did he buy altogether? 


(Big Unit) 
1 Strawberry = $2

(Small Unit)
1 Chocolate = 90% × $2 = $1.80

(Big Quantity : Small Quantity)
Strawberry : Chocolate
= 40 : 60 
= 2 : 3

(Rift Unit)
 3 Chocolate - 2 Strawberry
=  3 × $1.80 - 2 × $2
= $1.40

(Rift Quantity)
$30.80 ÷ $1.40 = 22

(Group Unit) 

3 + 2 = 5

Total Quantity = 22 × 5 = 110