Question

This sign shows when a lift is safe to use.
Total mass of people must be 480 kg or less
Fred and some other people are in the lift and their total mass
is 565 kg to the nearest 5 kg.
Fred, who has a mass of 88 kg to the nearest kg, gets out of the lift.
Is the lift now safe to use?
You must show your working and clearly state 'Yes it is safe' or 'No it is not safe'.

Answer 1

Step 1: Determine possible actual mass before Fred gets out
If the total mass is 565 kg to the nearest 5 kg, the actual mass could be anywhere from:

562.5 kg to 567.4 kg

Step 2: Determine possible actual mass of Fred
Fred's mass is 88 kg to the nearest kg, so it could be anywhere from:

87.5 kg to 88.4 kg
Step 3: Subtract Fred's possible mass from total mass
To find the minimum possible remaining mass:

Minimum total mass - Maximum Fred's mass
= 562.5 kg - 88.4 kg = 474.1 kg

To find the maximum possible remaining mass:

Maximum total mass - Minimum Fred's mass
= 567.4 kg - 87.5 kg = 479.9 kg

Step 4: Check if remaining mass is within the limit
The remaining mass after Fred gets out is between 474.1 kg and 479.9 kg, which is less than or equal to 480 kg.

Answer: Yes it is safe.