Find the missing number! Speed based competitive tests always have questions on finding missing numbers. Generally, these questions have some application of mathematical operations. Occasionally, these can also have symbols or letters. Look at these questions as puzzles and try to crack the logic. In this post, we will go through 10 questions on finding missing number. I am also adding my solutions to these questions. Through these questions, we will look at various methods of solving the same question (wherever possible) and understand what’s best in the exam situation. For most of the questions, I am not providing options so that you develop the ability to crack these questions without any support/guesswork using options.
Q.1 – Find the missing number:
Solution: The first line of attack would be understanding if multiplying adjacent numbers and adding products takes us to the middle number. 2*4 + 3*2 = 14. Doesn’t work. What else can we do? We need to go higher. If we take squares of outside numbers and add? 4 + 9 + 4 + 16 = 33. 9 + 16 + 25 + 4 = 54. Hence, the answer will be 36 + 9 + 16 + 25 = 86
Q.2 – Find the missing number:
Solution: Considering you have 24 and 576, the logic is fairly clear. It’s square of the number. If that doesn’t strike you, it is the product of all the numbers that are present in the image except the number in bottom right square. So 4*6*24 = 576. Similarly, 3*5*15 = 225
Q.3 – Find the missing number:
Solution: If we take the vertical sum, we will get 23 in the first column, 23 in the last column. Hence, the missing number will be 23 – (8 + 2) = 13. Even if you take the horizontal sum, you will get the same summation. Hence, 23 – 10 = 13 will be the answer.
Q.4 – Find the missing number:
Solution: When you see 17 and Q in a question, the logic becomes obvious. Q is the 17th letter. And then I can check if it is working in the second row. B is the second letter. So, I just need to find the 8th letter which is H and E is the fifth letter. Hence, we will have H and 5 in the place of question marks.
Q.5 – If 49*94 = 676, 65*59 = 625, What will be 99*95?
Solution: Here, 676 and 625 are squares so the logic has to be about square roots. If I take sum of digits of each of the numbers, 4 + 9 + 9 + 4 = 26 and 26^2 = 676. Hence, the answer will be 9 + 9 + 9 + 5 = 32^2 = 1024.
Q.6 – Find the missing number:
Solution: Here, as you look at these numbers, Sum of the first two rows minus the third row gives you the fourth row. (8 + 7) – 2 = 13; (3 + 6) – 4 = 5. Hence, (4 + 1) – ? = 4. The missing number is 1.
Q.7 – Find the missing number:
Solution: With 9 in the middle and 50 and 31, the logic has to be summation of the first and the third column. 9*9 = (50 + 31); 7*9 = (42 + 21). Hence, 43 + 11 = 54 and 54/9 = 6. The missing number is 6.
Q.8 – Find the missing number:
Solution: Here, if you add the squares of the smaller numbers, you get the bigger number. So 2^2 + 4^2 = 20. 7^2 + 5^2 = 74. So, 6^2 + 1^2 = 37 will be the missing number.
Q.9 Find the missing number:
Solution: Here, the numbers in the middle square are clearly squares so the logic should be related to square roots. If we take square roots, we get 6, 2, and 7. 6*2 = 12. 2*7 = 14. So, the logic is square roots and product of adjacent square roots to get the numbers outside. So 35 = 5*7. hence, the missing number will be 5^2 = 25. It will also satisfy the remaining part 6*5 = 30
Q.10 Find the missing number:
Solution: Another nice question. In all these questions, knowing the positions of letters helps. So T = 20, D = 4. The difference of which is the outside number. But note that it is the outer letter – inner letter that gives the number. So, H – K is what you are supposed to find. 8 – 11 = -3 will be the answer.
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