Beth is $b$ years old. Sam is 4 years younger than Beth. The product of their ages is 621 .
a) Show that $b^{2}-4 b-621=0$.
b) Work out Sam's age.

Answer

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Answer

$\boxed{19}$

Steps

Step 1 ：$b(b-4)=621$

Step 2 ：$b^{2}-4b=621$

Step 3 ：$b^{2}-4b-621=0$$\boxed{b^{2}-4b-621=0}$

Step 4 ：$b=23$ or $b=-27$

Step 5 ：Since age cannot be negative, $b=23$

Step 6 ：Sam's age is $b-4=23-4=19$

Step 7 ：$\boxed{19}$