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Worksheet Solutions: Maths Tricks - 1 | Mental Maths - Class 1 PDF Download

Q1: Find the number which exceeds 17319 by 1279
Ans:
17319+1279=18598
18598 is the required number


Q2: The sum of two numbers is 94506.One of the number is 49605. Find the other number.
Ans. 
Sum of the numbers=94506
One is 49605
Other one is 94506-49605=44901

Q3: What should be added o the sum of 346568 and 234263 to get the sum of 800000?
Ans. 
Step 1. 346568+234263=580831
Step 2. 800000-580831=219169 (ans)

Q4: Find the leat number which is exactly divisible by 12,15 and 20
Ans.
Least number = LCM of 12,15, 20 = 60 is the required number

Q5:  Find the largest number of 4-digits divisible by 12,15,18
Ans. 
Largest 4-digit number is 9999.
12 = 2*2*3
15 = 5*3
18 = 2*3*3
Lcm of 12,15,18 = 180
Now divide 9999 by 180, we get remainder as 99.
The required largest number=9999-99=9900(ans.)

Q6: In an election netween two candidates one got 55% of the total valid votes, 20% of the votes were invalid. If the total number of votes was 7500, find the number of valid votes that the other candidate got.
Ans.
Total number of votes = 7500
Valid votes = 80% = 80/100*7500
1st candidate got 55% of total valid votes, so 2nd candidate got 45% of total valid votes = 7500*(80/100)*(45/100)=2700(ans.)

Q7: If 20% of a=b, then b% of 20 is what?
Ans.
20%of a=b
=(20/100)*a=b
B% of 20= (b/100)*20= [(20a/100)/ 100]*20=4a/100=4% of a.(ans.)

Q8: A student multiplied a number by 3/5 instead of 5/3. Wha is the percentage error in the calculation?
Ans.
Let the number be x.
The correct ans should be 5x/3
By mistake it was 3x/5
Then, error = (5x/3-3x/5)=16x/15
Error %=(error/true value)*100= [(16/15)*x/(5/3)*x]*100=64% (ans.)

Q9: The length and breadth of a rectangle are(3a+2) and (2a-1). What is the perimeter?
Ans. Perimeter = 2(3a+2+2a-1) = 2(5a+1)(ans.)

Q10: The difference between the length and breadth of a rectangle is 8cm and the perimeter is 64cm. Find length and breadth.
Ans.
Length = x cm
Breadth = (x-8)cm
Perimeter = 2(x+x-8)=2(2x-8)
Given = 2(2x-8)=64cm
=2x-8=64/2=32
=2x=32+8=40
=x=40/2=20
Length=20cm
Breadth=20-8=12cm(ans.)

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