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Question

A had 180 more cookies than B at first. After A sold 80% of her cookies and B sold 30% of her cookies, B had twice as many cookies as A left. How many cookies did A have at first ?

Answer

This is a Before After question. 

   Before    Transfer After    
A    100u + 180 – 80u – 144   20u + 36
B   100u – 30u 70u
       

(20u + 36) / 1  = 70u / 2

20u + 36 = 35u

36 = 35u – 20u

15u = 36

5u = 36 ÷ 3 = 12

100u = 12 × 20 = 240

240 + 180 = 420

 

 

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At first —

A : 10 units + 180
B : 10 units

After —
A : 10 units – 80% x (10 units + 180) = 2 units + 36
B : 10 units – 30% x 10 units = 7 uniys

7 units = (2 units + 36) x 2 = 4 units + 72
1 unit = 72/(7 – 4) = 24
10 units + 180 = 10 x 24 + 180 = 420

Ans : 420 cookies.

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