How to subtract odd numbers - ACT Math

Card 0 of 4

Question

Tom has twice as many chores as Jeff, who has 3 less than Steve. Steve has 10 chores. How many chores does Tom have?

Answer

If Steve has 10 chores, Jeff has 7 chores (3 less than Steve). Tom has twice as many as Steve, so Tom has 14 chores.

Compare your answer with the correct one above

Question

Your mom made cookies. You ate , your brother ate twice as many as you did, and your sister ate . How many are left?

Answer

Create an equation for the situation described and solve:

$\text{Total Cookies - #you ate -#your brother are -#your sister ate}=\text{Cookies Left}$

$Total=38, You=7, Brother=2\cdot 7, Sister=5$

$38- 7 - (2 \cdot 7) - 5 = 38-7-14-5=12$

Compare your answer with the correct one above

Question

Your mom gives out total presents each year to your cousins. If your cousin Sally received and your cousin Billy received times as many as Sally, how many did your cousin, Becky get?

Answer

Create an equation to decribe the above situation and solve.

Total presents given out is represented by .

Presents given to Sally is represented by .

Presents given to Billy is represented by $B=3\cdot S=3\cdot 5=15$ .

Thus our equation becomes,

Compare your answer with the correct one above

Question

$\textup{Which of the following must be true if }ab\textup{ is odd and }c-b\textup{ is even? Presume that }a\textup{,}b\textup{,and } c\textup{ are integers}$

Answer

Always start by gathering your facts. You know that if is odd, then neither of those numbers are even. (If either were, then the product would be even.) Now, the rules for subtracting are just like adding. If the difference of two numbers is even, then they must either both be odd or both be even. Thus if is even and we know that is odd, then we know that must be odd. Thus if is odd, it is also true that is even, for both and are even.

Compare your answer with the correct one above

Tap the card to reveal the answer