Measurement error is the positive difference between a measured amount and the actual amount.

For example, Diego measures a line segment as 5.30 cm. The actual length is 5.32 cm. The measurement error is 0.02 cm, because .

A percent decrease tells how much a quantity went down. It is written as a percentage of the starting amount.

For example, a store had 64 hats on Friday. It had 48 hats left on Saturday. The number of hats went down by 16.

This was a 25% decrease, because 16 is 25% of 64.

Percent error is a way to describe error as a percentage of the actual amount.

For example, a box is supposed to have 150 folders. Clare counts only 147 folders in the box. This is an error of 3 folders. The percent error is 2%, because 3 is 2% of 150.

A percent increase tells how much a quantity went up. It is written as a percentage of the starting amount.

For example, Elena had $50 in the bank on Monday. She had $56 on Tuesday. The amount went up by $6.

This was a 12% increase, because 6 is 12% of 50. 

A percentage is a rate per 100.

For example, a fish tank can hold 36 liters. There are 27 liters of water in the tank. The percentage of the tank that is full is 75%.

A repeating decimal has digits that keep going in the same pattern over and over. The repeating digits are marked with a line above them.

• The decimal representation for  is , which means 0.3333333 . . . .
• The decimal representation for is , which means 1.136363636 . . . .

A tape diagram is a group of rectangles put together to represent a relationship between quantities.

This tape diagram shows a ratio of 30 gallons of yellow paint to 50 gallons of blue paint.

This tape diagram represents the equivalent ratio of 15 gallons of yellow paint to 25 gallons of blue paint.

A unit rate is a rate per 1.

For example, 12 people share 2 pies equally. One unit rate is 6 people per pie, because . The other unit rate is  of a pie per person, because .