Hello Readers,
Here are some short tricks on Multiplication which might help you in Quant Section of every competitive exam. Hope you all like the post!
1. Multiplication using multiples
Assume that we should find out the result of 12 x 15.
12 x 15 (Here we can write this 15 as 5 x 3)
= 12 x 5 x 3 (now 12 x 5 becomes 60)
= 60 x 3 (For this you just calculate 3 x 6, that is 18 and add one Zero to it. that is 180)
2. Multiplication by distribution
Assume that we should find out the result of 12 x 17
12 x 17
(Here we can divide this 17 as 10+7. Here, multiplying 12 with 17 is same as multiplying 12 with 10 and 7 separately and then adding the results)
so, we can write it as
= (12 x 10) + (12 x 7)
= 120 + 84
= 204
3. Multiplication by "giving and taking"
12 x 47 (Here its little difficult for us to calculate the multiplication of 12 and 47 mentally. so just check for the ROUNDED number nearer to 47. Yes it is 50. so.....
= 12 x (50 - 3)
= (12 x 50) - (12 x 3) = 600 - 36
= 564
4. Multiplication by 5
If we have to multiply a number with 5, just divide the number with 2 and then multiply the result with 10. Confused? Its very simple step actually....
428 x 5 (Now just divide the number with 2)
= 428 x 1/2 = 214 (Now multiply it with 10)
= 214 x 10
= 2140 (This is our result)
What’s the logic behind this step?
Very simple.
Lets say the number is X.
Now we are dividing the number with 2. so here X becomes X/2.
And then we are multiplying it with 10. So it will become 10X / 2
Now cancel it with 2. so it becomes 10X / 2 = 5X = 5 multiplied by X. That’s it ;)
5. Multiplication by 10 ------------ just move the decimal point one place to the right
16 x 10
= 160
5.9 = 159
169.93 = 169.3
6. Multiplication by 50 ------ divide with 2 and then multiply by 100
Well, this is also same process as we did for 5. Here we should add an extra zero. That’s it
18 x 50
= (18/2) = 9
= 9 x 100
= 900
7. Multiplication by 100 -------- move the decimal point two places to the right
45 x 100
= 4500
8. Multiplication by 500-------- divide with two and multiply with 1000
21 x 500
= 21/2 x 1000
= 10.5 x 1000
= 10500
9. Multiplication by 25 ---------- use the analogy Rs 1 = 4 x 25 Paise
25 x 14 (just divide the 14 as 10+4)
= (25 x 10) + (25 x 4)
= 250 + 100 ---> Rs2.50 + Rs1
= 350
10. Here you can use another technique too. Which we have used for multiplication with 5.
Multiplication by 25 ----------- Divide by 4 and multiply by 100
36 x 25
= (36/4) x 100
= 9 x 100
= 900
11. Multiplication by 11 (if sum of digits is less than 10)
72 x 11
= 7+2 =9, it is Less than 10. so,
= place this term 9 between 7 &2
= 792 (That's the answer)
12. Multiplication by 11 (if sum of digits is greater than 10)
87 x 11
=> 8 + 7 = 15
because here 15 is greater than 10, first use 5 and then add 1 to the first term 8,
which gives you the answer
= 957
13. Multiplication of numbers ending in 5 with the same first terms (square of a number)
25 x 25
first term = (2 + 1) x 2 = 6
last term = 25
answer = 625 => square of 25
75 x 75
first term = (7 + 1) x 7 = 56
last term = 25
answer = 5625 => 75 square
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