Unit 6 · Algebra

Lan, Marco and Niki — Who Has What Now?

Lesson 9 of 24

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About this lesson

Three friends share marbles. One gives some to another. You know totals and a final equal-share condition. Work backwards: use the equal condition to find one person's yesterday count, then subtract to find the rest.

Chapters

0:00Introduction
0:24The Question
1:01Isolating Niki's initial count
1:29Tracking the current state
1:54Reconstructing the complete balance sheet
2:21Solving for the final target sum
2:42Exam strategy — the conservation of mass shortcut
3:28Confirming the final option

Question

Yesterday, Lan, Marco and Niki had 26 marbles in total.

Lan and Marco had 20 marbles in total.

Today, Marco gave 5 of his marbles to Niki.

Now Marco and Niki both have the same number of marbles.

How many marbles do Lan and Niki have in total now?

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