Using Mental Math
Estimating Products
Multiplying 2-Digit Numbers by Multiples of 10
100
25 x 10
250
100
Use rounding to solve: 42 x 73 =
40 x 70 = 2,800
100
20 x 51 =
1,020
200
80 x 500 =
40,000
200
Use rounding to solve: 602 x 43 =
600 x 40 = 24,000
200
32 x 30 =
960
300
50 x 1,000 =
50,000
300
Use rounding to solve: 327 x 18 =
300 x 20 = 6,000
300
88 x 30 =
2,640
400
25 x 400 =
10,000
400
Estimate to decide which has a greater product, 39 x 21 or 32 x 32. Explain.
39 x 21 is about 40 x 20, which is 800. 32 x 32 is about 30 x 30, which is 900. Therefore, 32 x 32 is greater.
400
52 x 50 =
2,600
500
There are 9 players on each 4th grade basketball team in the Dublin City Schools league. What is the total number of players in the league if there are 30 teams? Use pictures, numbers, or words to show your answer.
9 x 30 = 270 players I multiplied the number of players by the number of teams to get the total number of players in the Dublin City Schools league.
500
A wind farm generates 330 kilowatts of electricity each day. About how many kilowatts does the wind farm produce in a week? Explain your answer using pictures, numbers or words.
330 rounds to 300 and there are 7 days in a week, so 7 x 300 = 2,100. Therefore, the wind farm produces ABOUT 2,100 kilowatts in one week.
500
Shivani and Lisa work as teacher assistants at Ohio State University. They earn $20 an hour! How much do they make altogether if they work 32 hours? Use pictures, numbers or words to explain your answer.
$20 x 32 hours = $640 per person. Since there are two people we need to double (or multiply by 2) $640. That equals $1,280. Therefore, they made $1,280 altogether.
M
e
n
u