Jim is saving his pocket money to buy a new toy. Jim has already saved seven pounds 30. The toy costs 12 pounds 90. Each week, Jim’s parents give him two pounds pocket money. Jim spends 30 percent of the pocket money he receives on sweets. Jim saves the rest of his pocket money to buy the toy. How many more weeks does Jim have to save for him to be able to buy the toy?
We know that this toy costs 12 pounds 90. And that Jim has already saved seven pounds 30. The first thing we should do is subtract seven pounds 30, the amount he saved, from the 12 pounds 90 that he needs. We can line them up vertically and then subtract. Zero minus zero is zero. Nine minus three is three. Bring down the decimal. 12 minus seven is five. The amount needed is five pounds 60.
The next piece of information we get is that every week he gets two pounds. However, Jim spends 30 percent of that on sweets. If 30 percent of that goes to sweets, then 70 percent of the two pounds is saved. And we need the amount that is saved every week. And so we take our 70 percent. And we write it as a decimal, 0.70. The word “of” means multiply. And so we need to take 0.70 and multiply it by two. This will tell us the amount that Jim saved each week.
To make this multiplication a bit easier, it’s now 0.10 times seven. Seventy hundredths or seven-tenths is equal to ten hundredths times seven. So we’ll now multiply 0.10 times seven times two. Seven times two is 14. And to multiply 14 by one-tenth, we move the digits one place to the right. 0.10 times 14 is 1.4. One-tenth of 14 is 1.4. That means that Jim saves one pound 40 each week.
If he can save one pound 40 each week, how many weeks until he has saved up the five pounds 60 that he needs. If we added two weeks together, he would have two pounds 80. And then if we add two weeks plus two weeks, this will give us the total for four weeks. Zero plus zero is zero. Eight plus eight is 16. Carry your one. Two plus two is four plus our one is five. In four weeks, Jim would have five pounds 60.
The question is asking the number of weeks. And so we answer four weeks.