# jochu/khan-exercises forked from Khan/khan-exercises

Use new cardinal helper for age word problems

1 parent ffb5469 commit af3e1e5b00a6f90754822f81e2c6acfe089b4c54 spicyj committed Jun 1, 2011
Showing with 9 additions and 9 deletions.
1. +9 −9 exercises/age_word_problems.html
18 exercises/age_word_problems.html
 @@ -19,7 +19,7 @@

person(1) is A years older than - person(2). B years ago, person(1) + person(2). Cardinal(B) years ago, person(1) was C times as old as person(2).

How old is person(1) now?

@@ -39,17 +39,17 @@

person(1) is A years older than - person(2). B years ago, person(1) + person(2). Cardinal(B) years ago, person(1) was C times as old as person(2).

How old is person(2) now?

(A - B + C * B) / (C - 1)
-
+

Let person(2)'s current age be personVar(2).

That means that person(1) is currently personVar(2) + A years old and B years ago, person(1) was (personVar(2) + A) - B = personVar(2) + A - B years old.

-

B years ago, person(2) was personVar(2) - B years old.

+

Cardinal(B) years ago, person(2) was personVar(2) - B years old.

person(1) was C times as old as person(2), so that means personVar(2) + A - B = C (personVar(2) - B).

Expand: personVar(2) + A - B = C personVar(2) - C * B.

Solve for personVar(2) to get C - 1 personVar(2) = A - B + C * B; personVar(2) = (A - B + C * B) / (C - 1).

@@ -91,7 +91,7 @@
A / (C - 1)
-
+

Let person(2)'s age be personVar(2).

We know person(1) is C times as old as person(2), so person(1)'s age can be written as C personVar(2).

His(1) age can also be written as personVar(2) + A.

@@ -108,7 +108,7 @@
-

person(1) is A times as old as person(2). B years ago, person(1) was C times as old as person(2).

+

person(1) is A times as old as person(2). Cardinal(B) years ago, person(1) was C times as old as person(2).

How old is person(1) now?

@@ -121,16 +121,16 @@
-

person(1) is A times as old as person(2). B years ago, person(1) was C times as old as person(2).

+

person(1) is A times as old as person(2). Cardinal(B) years ago, person(1) was C times as old as person(2).

How old is person(2) now?

B * (C - 1) / (C - A)
-
+

Let person(2)'s age be personVar(2).

We know person(1) is A times as old as person(2), so person(1)'s age can be written as A personVar(2).

-

B years ago, person(1) was A personVar(2) - B years old and person(2) was personVar(2) - B years old.

+

Cardinal(B) years ago, person(1) was A personVar(2) - B years old and person(2) was personVar(2) - B years old.

At that time, person(1) was C times as old as person(2), so we can write A personVar(2) - B = C (personVar(2) - B).

Expand: A personVar(2) - B = C personVar(2) - B * C.

Solve for personVar(1) to get C - A personVar(1) = B * (C - 1); personVar(1) = B * (C - 1) / (C - A).