Decimals of non-decimal units

The idea

A decimal of a unit such as an hour or a foot means tenths, hundredths, … of that unit, so it is converted using the unit's own sub-units (60 minutes, 12 inches), not read directly as minutes or inches.

The bus message

Sarayu gets a message: “The bus will reach the station 4.5 hours after noon.”

When will the bus reach the station?

• 4:05 p.m.
• 4:30 p.m.
• 4:50 p.m.

Two scales, one pin

The scale below is split in tenths of the unit. The scale above is split in the unit’s own parts (minutes or inches). Move the pin and read both.

Use the unit’s own parts

A decimal of an hour or a foot means tenths, hundredths… of that unit. To change it into minutes or inches, use the unit’s own parts: 60 minutes in an hour and 12 inches in a foot.

“Overs left: 5.5” means 5 overs and 5 balls, because 1 over is 6 balls. It is not 5 and a half overs.

A decimal of a unit such as an hour or a foot means tenths, hundredths, … of that unit, so it is converted using the unit’s own sub-units (60 minutes, 12 inches), and not read directly as minutes or inches.

• Decimal | Meaning
• 4.5 hours | 4 hours + 5 tenths of 60 min = 4 hours 30 min
• 2.5 ft | 2 ft + 5 tenths of 12 in = 2 ft 6 in
• 2 ft 5 in | 2 5/12 ft, which is not 2.5 ft

Notes

A decimal of an hour or a foot is converted with the unit’s own parts: 4.5 hours = 4 hours 30 min, 2.5 ft = 2 ft 6 in. It is not read as minutes or inches.

Check yourself

How many minutes is 0.5 hour?

Answer: 30 min

0.5 hour is half an hour: 30 minutes.

A film is 1.5 hours long. How many minutes is that in all?

Answer: 90 min

1.5 hours = 60 min + 30 min = 90 minutes.

How many inches is 0.5 ft?

Answer: 6 in

0.5 ft = half of 12 inches = 6 inches. So a door 2.5 ft wide is 2 ft 6 in.

A bus arrives 3.1 hours after noon. When does it arrive?

• 3:06 p.m. — correct. Yes! 0.1 hour is one-tenth of 60 minutes: 6 minutes.
• 3:10 p.m.. That reads 0.1 hour as 10 minutes. One-tenth of 60 minutes is 6 minutes.
• 3:30 p.m.. 3:30 p.m. would be 3.5 hours.