Question 1187442
Please help me with this math question on fraction.Thank you in advance.
{{{3/20}}} of the bottled water in a supermarket were sold on Monday.
90 fewer bottles of water were sold on Tuesday than on Monday. 70
fewer bottles of water were sold on Wednesday than on Tuesday. On
Thursday, 330 bottles of water were sold. The number of bottles of 
water left in the supermarket was {{{1/2}}} the number of bottles there was
at first. How many bottles of water were there in the supermarket at
first?
<pre>Let original number of bottles be B
Amount sold on {{{matrix(4,2, "Monday:", 3B/20, "Tuesday:", 3B/20 - 90, "Wednesday:", 3B/20 - 160, "Thursday:", 330)}}}

Total sold in 4 days: {{{matrix(1,3, 3B/20 + 3B/20 - 90 + 3B/20 - 160 + 330, "=", 9B/20 + 80)}}}

With {{{matrix(1,3, (1/2)B, or, B/2)}}} remaining, we can say that: {{{matrix(2,3, B - (9B/20 + 80), "=", B/2, B - 9B/20 - 80, "=", B/2)}}}
20B - 9B - 20(80) = 10B ------ Multiplying by LCD, 20 
     11B - 20(80) = 10B
         - 20(80) = 10B - 11B
         - 20(80) = - B
Original number of bottles, or {{{highlight_green(matrix(1,5, B, "=", (- 20)(80)/(- 1), "=", "1,600"))}}}</pre>