https://www.kiasuparents.com/kiasu/question/796692/
If you want to let your kid practice GuessandCheck, can try below. Total Qty is 120. As kids progress with more complex methods, they may drop the “troublesome” GuessandCheck method but it is still a good thing to practice once in a while until the big PSLE. Can also consider a little hybrid by making supposition (for every exchange) to save some time on guess and check. Still three sets of checking in below table.
$ per Tshirt 
Qty of Tshirts 
Total $ Tshirts 
$ per shorts 
Qty of shorts 
Total $ Shorts 
Diff 
$12.50 
let’s take 60 
$750 
$11 
60 
$660 
$90 

suppose 61 
$762.50 

59 
$649 
$113.50 

*see note 


*see note 

*see note 

69 
$862.50 

51 
$561 
$301.50 ok 
*analyse and deduce that for every one set of exchange from 1 pair of shorts to 1 Tshirt, Benny is spending $113.50$90 = $23.50 more on Tshirts. (Or save $11 + spend $12.50 = $23.50 more on Tshirts)
$301.50 – $113.50 = $188.00
$188.00 / $23.50 = 8 more exchanges (–> 598 = 51 pairs of shorts) (–> 61+8 = 69 Tshirts).
Put back into table and check*
(a) 51 pairs of shorts#
(b) $862.50 + $561= $1423.50#