The petrol tank of David's bus was 70% empty. He went to the petrol station and topped up 22 ℓ of petrol. When he reached the bank, the petrol tank was 80% full. Given that he used 7 ℓ of fuel to get to the bank from the kiosk, find the capacity of the petrol tank.
| |
Full |
Empty |
Total |
| Before |
3x1 =
3 u |
7x1 =
7 u |
10x1 =
10 u |
| Change 1 |
+ 22 |
- 22 |
|
| Change 2 |
- 7 |
+ 7 |
|
| After |
4x2 =
8 u |
1x2 =
2 u |
5x2 =
10 u |
70% =
70100 =
710 Empty : Total = 7 : 10
80% =
80100 =
45 Full : Total = 4 : 5
The full capacity of the petrol tank is unchanged.
Make the totals the same. LCM of 10 and 5 is 10.
Volume of petrol in the end
= 3 u + 22 - 7
= 3 u + 15
8 u = 3 u + 15
8 u - 3 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
