Question

solve for a: $a+b=c$
select one:
a. $a=c-b$
b. $a=b+c$
c. $b=c-a$
d. $a=b-c$

john is 4 years older than his sister mary. together, their ages add up to 30. how old is mary?
select one:
a. 14
b. 16
c. 17
d. 13

Explanation:

First Problem: Solve for $a$: $a+b=c$

Step1: Isolate $a$ by subtracting $b$

Subtract $b$ from both sides of the equation.
$a + b - b = c - b$

Step2: Simplify to solve for $a$

Cancel out $b$ on the left side.
$a = c - b$

Step1: Define variables for ages

Let $M$ = Mary's age, $J$ = John's age.
$J = M + 4$, $J + M = 30$

Step2: Substitute $J$ into sum equation

Replace $J$ with $M+4$ in the total age equation.
$(M + 4) + M = 30$

Step3: Simplify and solve for $M$

Combine like terms and isolate $M$.
$2M + 4 = 30$
$2M = 30 - 4 = 26$
$M = \frac{26}{2} = 13$

Answer:

a. $a=c-b$

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Second Problem: Mary's Age Calculation