The petrol tank of Brandon's bus was 80% empty. He went to the petrol station and topped up 42 ℓ of petrol. When he reached the bakery, the petrol tank was 85% full. Given that he used 3 ℓ of fuel to get to the bakery from the kiosk, find the capacity of the petrol tank.
| |
Full |
Empty |
Total |
| Before |
1x4 =
4 u |
4x4 =
16 u |
5x4 =
20 u |
| Change 1 |
+ 42 |
- 42 |
|
| Change 2 |
- 3 |
+ 3 |
|
| After |
17x1 =
17 u |
3x1 =
3 u |
20x1 =
20 u |
80% =
80100 =
45 Empty : Total = 4 : 5
85% =
85100 =
1720 Full : Total = 17 : 20
The full capacity of the petrol tank is unchanged.
Make the totals the same. LCM of 5 and 20 is 20.
Volume of petrol in the end
= 4 u + 42 - 3
= 4 u + 39
17 u = 4 u + 39
17 u - 4 u = 39
13 u = 39
1 u = 39 ÷ 13 = 3
Capacity of the petrol tank
= 20 u
= 20 x 3
= 60 ℓ
Answer(s): 60 ℓ
