The petrol tank of Neave's car was 60% empty. He went to the petrol kiosk and topped up 18 ℓ of petrol. When he reached the library, the petrol tank was 90% full. Given that he used 3 ℓ of fuel to get to the library from the kiosk, find the capacity of the petrol tank.
| |
Full |
Empty |
Total |
| Before |
2x2 =
4 u |
3x2 =
6 u |
5x2 =
10 u |
| Change 1 |
+ 18 |
- 18 |
|
| Change 2 |
- 3 |
+ 3 |
|
| After |
9x1 =
9 u |
1x1 =
1 u |
10x1 =
10 u |
60% =
60100 =
35 Empty : Total = 3 : 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
= 4 u + 18 - 3
= 4 u + 15
9 u = 4 u + 15
9 u - 4 u = 15
5 u = 15
1 u = 15 ÷ 5 = 3
Capacity of the petrol tank
= 10 u
= 10 x 3
= 30 ℓ
Answer(s): 30 ℓ
