Grades 1-2 Video Solutions 2020-2020Levels12prob14

Video Transcription

Problem number 14. Mary wants to write the numbers 1, 2, 3, 4, 5, and 6 inside the 6 squares of the figure.  She wants a different number in each square. She wants both the sums of the numbers in the blue squares and the sum of the numbers in the yellow squares to be 10.  What number must she write in the square of the question mark? A-1, B-2, C-3, D-4, E-5.  Often with a problem like this, you don't have to find the number that goes into every single one of the squares.  Here, the problem asks about what number should go in the square of the question mark, which is white.  But we know that the sum of the numbers in the yellow squares is 10, and the sum of the numbers in the blue squares is 10.  This means that the sum of all the numbers except the one of the question mark is 20. We also know which numbers Mary is going to use. 1, 2, 3, 4, 5, and 6.  And we can add those together to find the sum of all the numbers. 1 plus 2 plus 3 plus 4 plus 5 plus 6 is... 4 plus 6 is 10. 2 plus 3 is 5, plus 5 more is another 10, making 20.  And one more makes it 21. So we know that the sum of the 6 numbers that Mary writes is 21, and that the numbers on the yellow and blue squares add up to 20.  So we are left with the number that goes into the white square having to equal 1 to give us a sum of 21. So the answer is A-1.

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