7y + 10x = 99
y - x = 2
y = 7 , x = 5
Step-by-step explanation:
Let the two-digit number is 
<u>This can be written as:</u>
- 10x + y, where 1 ≤ x ≤ 9 and 0 ≤ y ≤ 9
<u>The difference between the number and product of its digits is:</u>
<u>Rewrite this as below:</u>
d = 10x - xy + y - 10 + 10 =
x(10 - y) - (10 - y) + 10 =
(x - 1)(10 - y) + 10
<u>We see that:</u>
- 0 ≤ x - 1 ≤ 8 according to the condition given above
- 1 ≤ 10 - y ≤ 10 again according to the condition given above
<u>The value of d is then:</u>
- 0 + 10 ≤ d ≤ 8*10 + 10
- 10 ≤ d ≤ 90
<h3>Proved</h3>
Answer: 10 minutes
Step-by-step explanation:
First you have to find out how big the tank is. You will have to you the formula Length x Width x Height. 20 x 18 x 10= 3,600 in. Then you would divide that by 360. 3,600/360= 10. It would have to take 10 minutes to empty the aquarium.