The petrol tank of Tommy's lorry was 75% empty. He went to the petrol station and topped up 25 ℓ of petrol. When he reached the cinema, the petrol tank was 85% full. Given that he used 1 ℓ of fuel to get to the cinema from the kiosk, find the capacity of the petrol tank.
| |
Full |
Empty |
Total |
| Before |
1x5 =
5 u |
3x5 =
15 u |
4x5 =
20 u |
| Change 1 |
+ 25 |
- 25 |
|
| Change 2 |
- 1 |
+ 1 |
|
| After |
17x1 =
17 u |
3x1 =
3 u |
20x1 =
20 u |
75% =
75100 =
34 Empty : Total = 3 : 4
85% =
85100 =
1720 Full : Total = 17 : 20
The full capacity of the petrol tank is unchanged.
Make the totals the same. LCM of 4 and 20 is 20.
Volume of petrol in the end
= 5 u + 25 - 1
= 5 u + 24
17 u = 5 u + 24
17 u - 5 u = 24
12 u = 24
1 u = 24 ÷ 12 = 2
Capacity of the petrol tank
= 20 u
= 20 x 2
= 40 ℓ
Answer(s): 40 ℓ
