Question

Check that 7 divides the sum 14 + 21 + 28.​

Answer 1

Observed that 7 is a divisor of 14, 21 and 28.

So in effect:

`\bold{14 = 7 * 2}`

`\bold{21 = 7 * 3}`

`\bold{28 = 7 * 4}`

Thus, adding member by member the previous equalities, we would have:

`\bold{14 + 21 + 28 = 63 = 7 * 2 + 7 * 3 + 7 * 4}`

Taking out the common factor of 7 in the previous expression, we will have:

`\bold{4 + 21 + 28 = 7 * 9}`

I mean:

`\bold{14 + 21 + 28 = 7 * 9}`

That is to say, that 7 is a divisor of the sum
`\bold{14 + 21 + 28}` since it is contained exactly 9 times in said sum.