# This Equals Twenty! Mental Math Activities for Second Grade

When mental math is required, the best technique to accomplish this objective is practice…practice…practice. But how do you keep the students interested when practicing this skill? Make it fun! Here are several activities that are quick, easy and effective.

## Objective

Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know from memory all sums of two one-digit numbers.** **MA2-OA-B-2

## Materials

- Decks of playing cards (Without the face cards)
- Blank bingo papers with sixteen squares and poker chips (or similar items to mark each square when playing)
- Scrap paper and pencils
- Store bought or handmade flash cards of addition and subtraction facts within twenty.
- Dice

## Activity One: “Five Wins”

Place students in groups of two or three. Give each student scrap paper and a pencil. The group should have one deck of cards (face cards removed).

- Each player should write any five numbers from 2-20 on their own paper. No number can be repeated.
- The players take turns. Player one turns over two cards, adds the numbers mentally and crosses off the answer if it appears on his paper. The other two players can challenge the answer if necessary.
- The first player to cross off all five of his own numbers wins.
- For a faster version when the two cards are turned over, all players add the two numbers mentally and cross off the number if it appears on their own papers.

## Activity Two: “Math Bingo”

- Instruct the students to randomly fill in a blank bingo card/paper with numbers from two through twenty. Numbers can be in any order and only used one time. There will not be enough squares to fill in every number.
- The teacher begins by holding up a flash card. Students mentally think of the answer and mark the appropriate square on their cards.
- Student who has a complete row marked either up and down, across, or diagonally wins and becomes the next leader to hold up the flash cards.

## Activity Three: “One and Out”

- Pairs of players each with a paper and pencil and one dice to share.
- Set the timer for one minute and then say “Start!”
- First player rolls the dice, rolls again adds it mentally to the first number and keeps a running total as he continues to roll.
*However*, if the player rolls a 1, they have to start over! - Second player does the same thing for one minute.
- The player with the highest total wins. Winner moves to another partner.

## Activity Four: “Find My Numbers”

- Teacher writes five numbers on the board where all students can see.
- For example the numbers might be: 13 4 8 5 10
- Place students in teams. One player from each team competes with a member of the other team. One point given for the team player that answers first.
- Then the teacher makes a statement like this:
- The sum of these two numbers is 14. (10,4)
- The difference between these two numbers is 4. (8-4 )
- The sum of these three numbers is 17 (4,8,5)
- Change the five numbers as needed to allow everyone to have a turn.

## Activity Five “Hit the Target”

- Pairs of students play this game. Each pair has one paper, pencil and one dice.
- If doing addition start with the number 0 (zero).
- If doing subtraction work down from 20.
- Write zero at the bottom of the paper and twenty at the top.
- First player rolls the dice and mentally adds it to zero and writes the sum above the zero.
- The second player rolls the dice and adds it to the first player’s number and writes the sum above that number. In other words there will be a column of numbers from zero and twenty.
- The first player to reach exactly 20 wins the game. You must roll the right amount without going over. Players may have to roll a few times to reach 20 exactly.

Example:

Player One rolls 4 (adding it mentally to zero, which equals 4)

Player Two rolls 3 (adding it mentally to 4, which equals 7)

Game continues until one person reaches 20 exactly.