NCERT Solutions for Class 4th Maths Chapter 10 Easy ways, comparing without calculating, and using a given answer — Let Us Solve
Book page 162 Updated on2026-09-19
Q1.
Find easy ways to solve the following problems. Write the answers in the given space. Share your thinking with the grade. a) 8787 – 99 b) 4596 + 104 c) 3459 + 21 d) 5010 + 95 e) 4990 + 310 f) 7844 – 15 g) 260 + 240 h) 1575 – 125 i) 3999 + 290
Answer
The trick is to make one number a round number first.
Sum
Easy way
Answer
a)
8787 − 99
Take away 100, then put 1 back: 8687 + 1
8688
b)
4596 + 104
4596 + 4 = 4600, then + 100
4700
c)
3459 + 21
3459 + 1 = 3460, then + 20
3480
d)
5010 + 95
5010 + 100 = 5110, then − 5
5105
e)
4990 + 310
4990 + 10 = 5000, then + 300
5300
f)
7844 − 15
7844 − 4 = 7840, then − 11
7829
g)
260 + 240
26 tens + 24 tens = 50 tens
500
h)
1575 − 125
1575 − 75 = 1500, then − 50
1450
i)
3999 + 290
3999 + 1 = 4000, then + 289
4289
Why it happens: Round numbers are easy to add and take away. We move
a little bit across, do the easy sum, and then put the little bit back.
Tip: If you add something extra to make a round number, remember to
take the same amount off at the end.
Q2.
Use the signs <, =, > as appropriate to compare the following without actually calculating. 54 + 97 ☐ 54 + 90
Answer
Both sides begin with the same number, 54.
54 + 97 > 54 + 90
Both sides start with 54.
On the left we add 97; on the right we add only 90.
97 is more than 90, so the left side is bigger.
Why it happens: When you add a bigger amount to the same number, you
end up with a bigger total. No need to work out the sums.
Q3.
84 – 68 ☐ 90 – 68
Answer
The same number, 68, is taken away on both sides.
84 − 68 < 90 − 68
Both sides take away 68.
We start from 84 on the left and from 90 on the right.
90 is more than 84, so more is left on the right.
Why it happens: Take the same amount from a bigger pile and a bigger
pile is left.
Q4.
76 + 85 ☐ 80 + 86
Answer
Both numbers on the right are bigger than the ones on the left.
76 + 85 < 80 + 86
76 is less than 80
85 is less than 86
Both parts on the left are smaller, so the total is smaller.
Why it happens: If each part grows, the total must grow too.
Q5.
73 – 54 ☐ 73 – 56
Answer
The same number, 73, on both sides. Notice what is being taken away.
73 − 54 > 73 − 56
Both sides start from 73.
On the left we take away 54; on the right we take away 56.
We take away less on the left, so more
is left.
Why it happens: Out of the same basket, take fewer mangoes and more
mangoes stay behind.
Check it yourself: 73 − 54 = 19 and 73 − 56 = 17.
19 is bigger.
Q6.
Use the given information to find the values. 139 + 175 = 314, so 314 – 175 = ______
Answer
139 + 175 =
314
314 − 175 =
______
314 − 175 = 139
139 and 175 were put together to make 314.
Take 175 back out, and 139 is what is left.
Why it happens: Adding and subtracting undo each other. No fresh
working is needed.
Q7.
845 – 394 = 451, so 845 – 395 = ______
Answer
845 − 394 =
451
845 − 395 =
______
845 − 395 = 450
We start from the same 845.
Now we take away 1 more than before (395 instead of 394).
So 1 less is left: 451 − 1 = 450
Why it happens: Take away one extra and you are left with one
less.
Q8.
354 + 167 = 521, so 354 + 168 = ______
Answer
354 + 167 =
521
354 + 168 =
______
354 + 168 = 522
354 stays the same.
168 is 1 more than 167.
So the answer is 1 more: 521 + 1 = 522
Why it happens: Add one more to a part and the total goes up by
one.
Q9.
456 + 209 = 665, so 446 + 219 = ______
Answer
456 + 209 =
665
446 + 219 =
______
446 + 219 = 665 — the same answer.
446 is 10 less than 456.
219 is 10 more than 209.
The 10 that left one number joined the other, so the total does not change.
Why it happens: Moving 10 from one side to the other is like moving
10 marbles between two bowls. The number of marbles altogether stays the same.