Estimation Skills

Work the shortcut one step at a time.

1. 01

   10% = 4.70

   Run the partial calculation — running total 4.7.

2. 02

   take 80% of that

   Apply this piece of the shortcut — running total 4.7.

3. →

   = ≈ $3.88

Left-to-right multiplication (Benjamin): break the 2-digit number into tens + units, multiply each, add.

1. 01

   60 × 6 = 360

   Tens first — biggest piece always goes first to keep the running total anchored.

2. 02

   7 × 6 = 42

   Now the units piece.

3. 03

   360 + 42 = 402

   Add the two partial products — left-to-right addition.

4. →

   = 402

Benjamin, Secrets of Mental Math — distribute by place

Left-to-right multiplication (Benjamin): break the 2-digit number into tens + units, multiply each, add.

1. 01

   50 × 8 = 400

   Tens first — biggest piece always goes first to keep the running total anchored.

2. 02

   3 × 8 = 24

   Now the units piece.

3. 03

   400 + 24 = 424

   Add the two partial products — left-to-right addition.

4. →

   = 424

Benjamin, Secrets of Mental Math — distribute by place

×5 shortcut (Benjamin): multiply by 10, then halve.

1. 01

   61 × 10 = 610

   Stick a zero on the end first (because 61 is odd, halving last is cleaner).

2. 02

   610 ÷ 2 = 305

   Halve the result.

3. →

   = 305

Benjamin, Secrets of Mental Math — distribute by place

Left-to-right multiplication (Benjamin): break the 2-digit number into tens + units, multiply each, add.

1. 01

   30 × 4 = 120

   Tens first — biggest piece always goes first to keep the running total anchored.

2. 02

   0 × 4 = 0

   Now the units piece.

3. 03

   120 + 0 = 120

   Add the two partial products — left-to-right addition.

4. →

   = 120

Benjamin, Secrets of Mental Math — distribute by place