Iam having trouble with multiplying negative numbers and positive numbers

So, negatives are tricky. But here's a nice rule for it:

1). negative (-) times negative (-) is positive because like signs, when multiplied are always positive.

2). negative (-) times positive (+) is negative because, different signs, when multiplied, are always negative.

3). positive (+) times positive (+) is positive because, again, like signs, when multiplied, are always positive.

Let's do the first 2 together:

So -5 times 7. First, let's ignore the signs and do the numbers first. 5 * 7 = 35. Cool. Now lets do the signs. Since it's a negative times a positive, it'll be negative. So your answer is -35.

Now lets do -8 times -4. Ignore the signs. 8 * 4 = 32. Now the signs. It's negative times negative. So it'll be positive because like signs, when multiplied, will always be positive. So the answer to the second one is 32.

Hope this helps!!

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms

hey there!

mass = 6.75 g

volume =   9 cm³

therefore:

d = mass / volume

d   = 6.75 / 9

d = 0.7 g/cm³

answer b