Quickly estimate a result by ,[object Object], numbers.

[object Object],:

• •Check if a result makes sense
• Calculate mentally
• •Detect errors

[object Object],: 47 × 23

• Round: 50 × 20 = 1000
• •Exact calculation: 1081
• •The order of magnitude helps verify!

[object Object],: 198 + 403

• Round: 200 + 400 = 600
• •Exact calculation: 601

In what order should calculations be performed?

PEMDAS Rule

1. •[object Object],arentheses ()
2. •[object Object],xponents (powers)
3. •[object Object],ultiplication and ,[object Object],ivision (left to right)
4. •[object Object],ddition and ,[object Object],ubtraction (left to right)

Examples

[object Object],: 5 + 3 × 2

• First do multiplication: 3 × 2 = 6
• Then addition: 5 + 6 = ,[object Object]
• ❌ Not (5+3) × 2 = 16!

[object Object],: 20 - 10 ÷ 2

• First division: 10 ÷ 2 = 5
• Then subtraction: 20 - 5 = ,[object Object]

[object Object],: (8 + 2) × 3

• First parentheses: 8 + 2 = 10
• Then multiplication: 10 × 3 = ,[object Object]

[object Object],: 2 + 3 × (4 + 1)

1. Parentheses: 4 + 1 = 5
2. Multiplication: 3 × 5 = 15
3. Addition: 2 + 15 = ,[object Object]

[object Object]

1. Parentheses: 10 - 2 = 8
2. Exponent: 3² = 9
3. •Multiplication and division:, ,[object Object],
4. Addition and subtraction:, ,[object Object],

[object Object]

• •[object Object],arentheses
• •[object Object],xponents
• •[object Object],ultiplication/,[object Object],ivision
• •[object Object],ddition/,[object Object],ubtraction