Grades 1-2 Video Solutions 2022-2022_1-2

Video Transcription

Problem number 17. The sum of the five numbers in each house is 20. Some numbers have been painted over. What number is hidden under the question mark? A3, B4, C7, D9 or E14.  The sum of the numbers on the darker house is 20. And the sum of the numbers on the lighter house is 20.  We see that the houses have these two numbers in common.  We can go about solving this problem two ways. We can either find out what the two numbers that  are shared are and use that to figure out the number of the question mark. Or we can notice  that because these two numbers that we don't know in the middle here are the same for both houses,  the sum of the remaining numbers on each house has to be the same.  We can think of it this way. 5 plus 2 plus 6 plus the green numbers is the same as the green numbers plus 3 plus question mark plus 1.  Since the green numbers on both sides, we can just ignore them.  And we have 5 plus 2 plus 6, which is 13,  is equal to 3 plus question mark plus 1, which is the same as 4 plus the question mark.  And what number added to 4 gives us 13? It's 9. So the question mark is equal to 9. The number 9 is right here. The answer is D.

Video Summary

The problem involves two houses where the sum of numbers in each house is 20, and two numbers are shared between both. The task is to find the number hidden under a question mark. By equating the remaining sum of unshared numbers from both houses, which is 13 on one side, and represented as 3 plus the question mark plus 1 on the other, the equation simplifies to 4 plus the question mark equals 13. Solving for the question mark, it turns out to be 9. Therefore, the hidden number is 9, and the correct answer is option D.