Mrs Yang had a sum of money. She gave her daughter $800 and gave ¹₆ of the remaining money to her son. She used ³₄ of the rest of the money on a computer and was left with ¹₈ of the amount she had at first. What was the sum of money she had at first?

Her daughter	Her son	Remaining amount		Total
$800	1x4	5x4
		Computer	Left
		3x5	1x5
7x5 = 35 u			1x5 = 5 u
16 u	4 u	15 u	5 u	40 u

Fraction of the remaining amount left 
= 1 - ³₄
= ¹₄

The remaining amount is repeated.  Make the remaining amount the same. LCM of 5 and 4 is 20. 

The amount left is repeated.  Make the amount left the same.

¹₄ Remaining amount = ¹₈ Total amount

Amount that Mrs Yang gave to her daughter
= 35 u - 4 u - 15 u
= 16 u

16 u = 800

1 u = 800 ÷ 16 = 50

Total amount that Mrs Yang had at first
= 16 u + 4 u + 15 u + 5 u
= 40 u
= 40 x 50
= $2000

Answer(s): $2000