Mental Math: Percent David McKillop Making Math Matter, Inc.

Mental Math: Per cent (The 1% Strategy) When a quantity is distributed equally among the 100 cells in this grid, the amount in each cell is 1% of this quantity. Therefore, divide a quantity by 100 to get 1%.

Mental Math: Per cent (The 1% Strategy) For example, to find 1% of $800, divide $800 by 100 to get $8 in each cell which is 1%. So, 1% x $800 = $8. To find 3% of $800, you would just multiply $8 by 3 to get $24. So, 3% x $800 = $24.

Mental Math: Per cent (The 1% Strategy) Find: 1% of $600 1% of $1200 3% of $900 4% of $500

5 Mental Math: Per cent (The 10% Strategy) Finding 10% of a quantity is like finding the amount in 10 cells of this grid. Since there are ten rows of 10, 10% can be found by dividing the quantity by 10.

6 For example, to find 10% of $150, just divide $150 by 10 to get $15. Therefore, 10% x $150 = $15

7 Mental Math: Per cent (The 10% Strategy) Find: 10% of $70 10% of $300 10% of $250 10% of $1200

8 Mental Math: Per cent (Estimating 10% by rounding to the nearest “nice” number) Estimate: 10% of $ % of $ % of $289 10% of $137.89

9 Mental Math: Per cent (The 15% Strategy) Finding 15% of a quantity is like finding the amount in 15 cells of this grid. Since 5% is half of 10%, you can find 15% by finding 10%, taking half of that amount, and adding it to the 10%.

For example, to find 15% of $400, find 10% of $400 by dividing by 10 to get $40, take half of $40 to get $20, and add the $20 to the $40 to get a total of $60. Therefore, 15% x $400 = $60.

Mental Math: Per cent (The 15% Strategy) Find 15% of each of the following: $40 $80 $120 $600

Mental Math: Per cent (Estimate using the 15% Strategy) Estimate the 15% tax on each of the following costs: $61.25 $139 $ $789

Percents Mentally calculate 25%, 33 ⅓%, and 66 2/3% of quantities compatible with these percents Estimate percents of quantities

Visualization of Percent Find 3% of $800. Think: If $800 is distributed evenly in these 100 cells, each cell would have $8 – this is 1%. Therefore, there is 3 x $8 or $24 in 3 cells (3%).

Visualization of 25 Percent Find 25% of $800. Think: If $800 is distributed evenly in these 4 quadrants, each quadrant would have $800 ÷ 4 or $200. Therefore, 25% of $800 is $200.

Estmating Percent Estimate: 25% of $35 25% of $597 26% of $48 24% of $439 26% of $118 25% of $4378

Visualization of 33⅓% Percent Find 33⅓% of $69. Think: $69 shared among three equal parts would be $69 ÷ 3 or $23. Therefore, 33⅓% of $69 is $23.

Visualization of Percent Find 33⅓% of: $96 $45 $120 $339 $930 $6309

Estimating Percent Estimate: 33⅓% of $67 33⅓% of $91 33% of $180 34% of $629 32% of $ ⅓% of $8999

Visualization of 66⅔ Percent Find 66⅔% of $36. Think: $36 divided by 3 is $12, so each one- third is $12, Therefore, 2-thirds is $24, so 66⅔% of $36 is $24.

Visualization of 66⅔ Percent Find 66⅔% of: $24 $60 $120 $360 $660

Estimating Percent Estimate: 67% of $27 65% of $90 68% of $116 65% of $326 67% of $894