MENTAL MATH PRACTICE WORD PROBLEMS ADDITION AND SUBTRACTION

Problem 1 :

If a winter day has 10 hours of daylight, then the day has how many  hours of darkness ? (Hint : A whole day has 24 hours.)

Solution :

Winter day = 10 hours of daylight

Whole day = 24 hours

Number of hours of darkness = 24 - 10

Breaking down 24 as the sum of 10

= 14 + 10 - 10

= 14

So, 14 hours of darkness.

Problem 2 :

Twelve of the 25 students in the class were girls. How many boys were in the class ?

Solution :

Number of students = 25

Girls students = 12

Boys students = ?

= 25 - 12

= 13 + 12 - 12

= 13

So, 13 boys were in the class.

Problem 3 :

At 7 : 00 a.m. the air was cool, but by noon the temperature had increased 25 degrees to 68^ºF. What was the temperature at 7 : 00 a.m. ? 

Solution :

At 7:00 am, air temperature = 68º F

It is increased by 68º F

Difference between two temperature = 68 - 25

= 48 + 20 - (20 + 5)

= 48 - 5

= 43

So, the temperature at 7 : 00 a.m is 43 degrees.

Problem 4 :

Tamira read 6 pages before lunch. After lunch she read some more. If Tamira read 13 pages in all, how many pages did  she read  after lunch ? 

Solution :

Tamira read the total pages = 13 pages

Before lunch = 6 pages

After lunch = some more pages

6 + p = 13

p = 13 - 6

p = 7

So, 7 pages did she read after lunch.

Problem 5 :

The numbers 5, 9, and 14 form a fact family. Write two addition facts and two subtraction facts using these three numbers.

Solution :

Two addition facts :

If it is known that 5 + 9 = 14

Then it follows that 9 + 5 = 14.

Two subtraction facts :

14 - 9 = 5 and 14 - 5 = 9.

Problem 4 :

4 + 3 + 5 + 8 + 7 + 6 + 2

Solution :

Given, 4 + 3 + 5 + 8 + 7 + 6 + 2

= 2 + 3 + 4 + 5 + 6 + 7 + 8

= 9 + 5 + 6 + 7 + 8

= 9 + 1 + 4 + 6 + 7 + 8

= 10 + 10 + 7 + 8

= 20 + 15

= 35

Problem 5 :

If 3 + ▲ = 7 and if ■ = 5, then ▲ + ■ equals which of the following ?

A. 4      B. 5     C. 8    D.  9

Solution :

Given, 3 + ▲ = 7 and ■ = 5

3 + ▲ = 7

▲ = 7 - 3

▲ = 4

▲ + ■ = 4 + 5

▲ + ■ = 9

So, option D) is correct.

Problem 6 :

How many different odd three - digit numbers can you write using the digits 5, 0, and 9 ?

Each digit may be used only once, and the digit 0 may not be used in the hundreds place.

Solution :

To create odd number, we have to choose 9 or 5. Repetition is not allowed

__   ___   ___

To fill up the hundreds place, we have 2 options. 

To fill up the one's place, we have 1 option

To fill up the ten's position, we have 1 option.

So, total number numbers created using the the digits is 2.