Read the instruction twice
Most wrong answers in a grid question start before any arithmetic. The instruction names one kind of number, and a quick read swaps it for a kind next to it: the largest number instead of the largest even number, every odd number instead of every prime.
Read it once to see what you will do, and a second time to see exactly which numbers it names.
Mark the numbers, then compute
Scan the grid once for each number the instruction names, and mark it before you do anything else.
The highest even number is 28, not 29, which is odd. The lowest odd number is 3, not 2, which is even.
Only now work it out: 28 × 3 = 84.
A new instruction, the same grid
The next instruction for this grid is: add every prime number.
Read it twice, then decide which numbers you would mark before adding anything.
Try it
Which numbers do you mark for add every prime number?
- 5, 17, 3, 11, 29 and 2
- 9, 5, 17, 3, 11, 29 and 15
Show the answer
5, 17, 3, 11, 29 and 2
Correct. 2 is prime even though it is even, and 9 and 15 are odd but not prime. The sum is 5 + 17 + 3 + 11 + 29 + 2 = 67.
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Practice Grid arithmetic