The petrol tank of Riordan's sports car was 80% empty. He went to the petrol kiosk and topped up 38 ℓ of petrol. When he reached the school, the petrol tank was 90% full. Given that he used 10 ℓ of fuel to get to the school from the kiosk, find the capacity of the petrol tank.
|
Full |
Empty |
Total |
Before |
1x2 = 2 u |
4x2 = 8 u |
5x2 = 10 u |
Change 1 |
+ 38 |
- 38 |
|
Change 2 |
- 10 |
+ 10 |
|
After |
9x1 = 9 u |
1x1 = 1 u |
10x1 = 10 u |
80% =
80100 =
45 Empty : Total = 4 : 5
90% =
90100 =
910 Full : Total = 9 : 10
The full capacity of the petrol tank is unchanged.
Make the totals the same. LCM of 5 and 10 is 10.
Volume of petrol in the end
= 2 u + 38 - 10
= 2 u + 28
9 u = 2 u + 28
9 u - 2 u = 28
7 u = 28
1 u = 28 ÷ 7 = 4
Capacity of the petrol tank
= 10 u
= 10 x 4
= 40 ℓ
Answer(s): 40 ℓ