Exercise 1.2 - Chapter 1 Number Systems Term 1 7th Maths Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

Updated By SaraNextGen

On April 24, 2024, 11:35 AM

Ex $1.2$
Question $1 .$
Fill in the blanks
(i) $-44+\ldots=-88$
(ii) $-75=-45$
(iii) $-(+50)=-80$
Solution:
(i) $-44$
(ii) 30
(iii) $-30$

Question $2 .$
Say True or False.
(i) $(-675)-(-400)=-1075$
(ii) $15-(-18)$ is the same as $15+18$
(iii) $(-45)-(-8)=(-8)-(-45)$
Solution:
(i) False
(ii) True
(iii) False

Question $3 .$
Find the value of the following.
(i) $-3-(-4)$ using number line.
Solution:
We start at zero facing positive direction. Move 3 units backward to represent $(-3)$. Then turn towards the negative side and move 4 units backwards. We reach $+1$.

$\therefore(-3)-(-4)=+1$
(ii) $7-(-10)$ using number line
Solution:
We start at zero facing positive direction. Move 7 units forward to represent $(+7)$. Then turn towards the negative side and move 10 units backwards.
We reach $+17$

$\therefore 1-(-10)=+17$
(iii) $35-(-64)$
Solution:
$35-(-64)=35+($ Additive inverse of- 64$)=35+(+64)=99$
$\therefore 35-(-64)=99$
(iv) $-200-(+100)$
Solution:
$-200-(+100)=-200+($ Additive inverse of $+100)=-200+(-100)=-300$
$-200-(+100)=-300$

Question $4 .$
Kabilan was having 10 pencils with him. He gave 2 pencils to senthil and 3 to Karthick. Next day his father gave him 6 more pencils, from that he gave 8 to his sister. How many pencils are left with him?
Solution:
Total pencils Kabilan had $=10$
No. of pencils given to Senthil $=2$
No. of pencils given to Karthick $=3$.
Now number of pencils left with Kabilan $=10-2-3=8-3=5$
Number of pencils got from his father $=6$
No. total pencils Kabilan had $=5+6=11$
Number of pencils given to his sister $=8$
Number of pencils left with Kabilan $=11-8=3$

Question $5 .$
A lift is on the ground floor. If it goes 5 floors down and then moves up to 10 floors from there, then in which floor will the lift be?
Solution:
Initially the lift will be in the ground floor representing ' 0 ',
It goes to 5 floors down $\Rightarrow-5$
Then it moves 10 floors up $+10$.
Now the lift will be $=0-5+10=-5+10$
$=5^{\text {th }}$ floor (above the ground floor)

Question $6 .$
When Kala woke up, her body temperature was $102^{\circ} \mathrm{F}$. She took medicine for fever. After 2 hours it was $2^{\circ} \mathrm{F}$ lower. What was her temperature then?
Solution:
Kala's temperature initially $=102^{\circ} \mathrm{F}$
After two hours the temperature decreased $=-2^{\circ} \mathrm{F}$
Now the final temperature $=102^{\circ} \mathrm{F}-2^{\circ} \mathrm{F}=100^{\circ} \mathrm{F}$
 

Question $7 .$
What number should be added to $(-17)$ to get $-19 ?$
Solution:
According to the problem $=-17+$ A number $=-19$
The number $=-19+17=-2$
$\therefore-2$ should be added to $-17$ to get $-19$

Question $8 .$
A student was asked to subtract (-12) from -47. He got - 30. Is he correct? Justify.
Solution:
Subtracting $-12$ from $-47$, we get
$-47-(-12)=-47+($ Additive inverse of-12 $)$
$=-47+(+12)=-35$
But the students answer is $-30$.
So he is not correct.

Objective Type Questions
Question $9 .$
$(-5)-(-18)$
(i) 23
(ii) $-13$
(iii) 13

(iv) $-23$
Solution:
(iii) 131

Question $10 .$
$(-100)-0+100=$
(i) 200
(ii) 0
(iii) 100
(iv) $-200$
Solution:
(ii) 0